Why is there 1 carb per cylinder when a car has one carb for multiple cylinders?

Post by m***@merr.com
I'm an amateur just beginning to work on my own bikes (GS850L & CB450)
and I'm wondering if there are any multiple cylinder bikes that operate
with one carb like most cars do.? Thanks for any input

It's done on cars to save money. It doesn't do much for power output,
though.

Leon

Les

2006-06-11 05:26:20 UTC

Harley's use one carb, as well as some of the older British bikes. A
buddy has a Honda Goldwing that's running a 4 bbl Edlebrock carb made
for a car. Runs pretty good but has a slight hesitation when the 4 bbl
kicks in. He's rode it this way for several years now.

Les

The Older Gentleman

2006-06-11 07:33:21 UTC

Lots of twins did/do.

Gold Wings.

Kawasaki Z1300 six used three twin-choke carbs.

Early Suxuki GSX550/750 fours used a p[air of twin-chokes.

But not that many, agreed.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

SAMMM

2006-06-11 10:57:18 UTC

bikes often run at higher speeds than cars and the 'tuning'
of the intake tract becomes important then.
the pulse of the intake valve opening creates a 'wave' which
can increase the amount of air the cylinder will intake.

it's more complex than that but that's the general idea.
one carb per cylinder makes 'tuning' that 'wave' easier.
note some pricier cars have intake tracts that change length at higher rpm.
some older hondas such as the CA77 and CA72 used one carb for two
cylinders. these were the lower performance bikes.
they also had crankpins that were side-by-side so the intake pulses
were evenly timed.
the nearly identical engine in the CB77 et al. had 180 degree cranks
and needed two carbs.
sammmm

R. Pierce Butler

2006-06-11 12:58:14 UTC

It is rather difficult to fit a single carb with an intake manifold on a
bike.

The Older Gentleman

2006-06-11 17:15:39 UTC

It is rather difficult to fit a single carb with an intake manifold on a
bike.

(And not for the first time he posts this reply...)

Complete and utter nonsense.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

R. Pierce Butler

2006-06-12 13:07:30 UTC

Post by m***@merr.com
I'm an amateur just beginning to work on my own bikes (GS850L &
CB450) and I'm wondering if there are any multiple cylinder bikes
that operate with one carb like most cars do.? Thanks for any input

It is rather difficult to fit a single carb with an intake manifold on
a bike.

(And not for the first time he posts this reply...)
Complete and utter nonsense.

Cites please.

I would love to see someone put an intake maniford and a single carb on
something like a KZ-1300 and then tell me that it was easy.

James Clark

2006-06-12 15:10:53 UTC

R. Pierce Butler wrote:
Cites please.

Post by R. Pierce Butler
I would love to see someone put an intake maniford and a single carb on
something like a KZ-1300 and then tell me that it was easy.

Boss Hoss uses a single carburetor, and it has 2 more cylinders than the Kawasaki.

2006-06-12 18:25:50 UTC

Post by R. Pierce Butler
Cites please.

Post by R. Pierce Butler
I would love to see someone put an intake maniford and a single carb on
something like a KZ-1300 and then tell me that it was easy.

Boss Hoss uses a single carburetor and it has 2 more cylinders than the Kawasaki.

Major clue ahead:

The Chevy's single carburetor has *accelerator pumps* to overcome low
engine vacuum when the butterflies are suddenly opened. The Kawasaki
uses smaller inlet port runners to keep vacuum high for quicker
response. Motorcycle carbs have gotten along without accelerator pumps
for decades because the whole induction design concept is different.

The Boss Hoss has 5 times the displacement of the KZ-1300 and turns a
lot slower to put out half the horsepower per cubic inch. It probably
has a complicated manifold with long U-shaped runners feeding banks of
cylinders.It doesn't matter much to the Chevy engine that inlet port
velocity is low, since the mainfold runners are feeding from a larger
plenum chamber under the carburetor.

NASCAR tuners are even taking advantage of the fact that fuel droplets
condense and puddle in the bottom of the manifold. They regard the
puddle of gasoline as a sort of fuel reservoir to help the engine
accelerate when the butterflies first open.

Car drivers can put up with cantankerous throttle response because the
car has four wheels and it isn't going to throw the driver out the
window. But a motorcycle rider needs the smooth response that the
engineers have achieved using multiple CV carbs
and single intake runners.

If you compared the venturi area of the Kawasaki carburetors vs. the
Chevy carb, you'd probably find that the Kawasaki has more venturi area
per cubic inch, so it uses a different manifold/carburetor arrangement
to keep inlet port velocity high.

There's no room behind the KZ-1300's engine for long intake runners,
the space is needed for the airbox, which acts as a Helmholtz Resonator
to help smooth out the
midrange flat spot.

The Older Gentleman

2006-06-12 19:48:52 UTC

Post by FB
But a motorcycle rider needs the smooth response that the
engineers have achieved using multiple CV carbs
and single intake runners.

Jesus, in every bit of wisdom you post there's a huge steaming pile of
crap.

Like this: multiple-cylinder bikes manage to achieve smooth response
using ordinary slide carbs. There's one sitting in my garage right now.

I'll not argue that CV carbs manage to compensate for a lot of nasties,
but slide carbs still have a lot to offer.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-12 22:05:58 UTC

Post by FB
But a motorcycle rider needs the smooth response that the
engineers have achieved using multiple CV carbs
and single intake runners.

Jesus, in every bit of wisdom you post there's a huge steaming pile of
crap.

You don't have to call me "Jesus", you can call me "LeRoy". ;-)

And, there's no secret that some users surf through Usenet all day,
just looking for opinions to disagree with.

Post by The Older Gentleman
Like this: multiple-cylinder bikes manage to achieve smooth response
using ordinary slide carbs. There's one sitting in my garage right now.

Fine. You can use smaller bore, old Amals, or you can use larger bore
Mikuni and Keihin slide valve carbs and get good throttle reponse
because Mikunis have 5 circuits instead of 3.

Post by The Older Gentleman
I'll not argue that CV carbs manage to compensate for a lot of nasties,
but slide carbs still have a lot to offer.

Yes, I have a little GSXR-750 in the garage now. It has a set of 33mm
Mikuni roundslide smoothbores that I bought used. With a Yoshimura
competition pipe it probably has 20 horsepower more than stock and I
have startled GSXR-1100 riders with the accleration.

The old gixxer is a monster that takes careful throttle control, and is
no fun to ride slowly.

In order to tame it down, I jetted it lean and advanced the timing 5
degrees.

But, if I was going to do a carb swap on a later model GSXR, I would
spring for the RS-series radial flat slide carbs with accelerator pumps.

The Older Gentleman

2006-06-13 06:15:12 UTC

Post by The Older Gentleman
Jesus, in every bit of wisdom you post there's a huge steaming pile of
crap.

You don't have to call me "Jesus", you can call me "LeRoy". ;-)
And, there's no secret that some users surf through Usenet all day,
just looking for opinions to disagree with.

Nah, I agree with you just as much. See other thread. But, as an
illustration, that huge tome addressed to the guy with the dicky
CG125....

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-13 14:19:58 UTC

Post by FB
And, there's no secret that some users surf through Usenet all day,
just looking for opinions to disagree with.

Nah, I agree with you just as much. See other thread. But, as an
illustration, that huge tome addressed to the guy with the dicky
CG125....

Like I said before, I work from the presumption that anybody asking a
question to rec.motorcycles.tech knows very little about motorcycles,
but may have some misconceptions caused by his/her experience with
cars. So I take extra effort to start with the basics.

Too bad if that bothers you.

chateau.murray@btinternet.com,

2006-06-13 16:11:16 UTC

Post by FB
And, there's no secret that some users surf through Usenet all day,
just looking for opinions to disagree with.

Nah, I agree with you just as much. See other thread. But, as an
illustration, that huge tome addressed to the guy with the dicky
CG125....

No, it's fine, but if you were to start with the basics on a CG125 (and
bikes don't come any more basic), it would be a good idea to refer to
slide carbs rather than CVs, which it doesn't use (and never has).
Otherwise you wind up with something totally irrelevant and which has
the potential to confuse a newbie to the point where he starts acting
on incorrect advice.

It also has the side-effect of showing that you have zero familiarity
with the bike under discussion....

Scott

2006-06-13 01:14:25 UTC

Post by FB
The Chevy's single carburetor has *accelerator pumps* to overcome low
engine vacuum when the butterflies are suddenly opened. The Kawasaki
uses smaller inlet port runners to keep vacuum high for quicker
response. Motorcycle carbs have gotten along without accelerator pumps
for decades because the whole induction design concept is different.

My CB900F has an accelerator pump, but only one, on the #2 carb. FWIW.

-Scott

--
'73 CB450K
'82 CB900F (x2)
'04 FSC600 (SWMBO)

Ted Mittelstaedt

2006-06-13 05:30:15 UTC

Post by FB
There's no room behind the KZ-1300's engine for long intake runners,
the space is needed for the airbox, which acts as a Helmholtz Resonator
to help smooth out the
midrange flat spot.

Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

Ted

2006-06-13 14:23:48 UTC

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

What kind of motorcycle is it? Is it an inline-4? Does it have a
4-into-1 pipe? Or does it have a stock exhaust system with balance
tubes between the pairs of exhaust pipes? Do you only ride in straight
lines, with no slow corners?

Sean J Kelly

2006-06-13 15:43:51 UTC

Not to argue with you, but i also have a bike with pod filters and no
(noticeable) flat spots in the midrange. it's a honda cb350 twin
with stock
(CV?) keihin carbs and k&n pods.
of course, the stock air filters are just paper elements with a metal
casing. and the exhaust consists of two seperate headers leading to two
seperate mufflers. no cross-over of exhaust gases at all.

But I've never had it on a dyno, so perhaps my perception is off.

-Sean

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

2006-06-13 16:21:31 UTC

Post by Sean J Kelly
Not to argue with you, but i also have a bike with pod filters and no
(noticeable) flat spots in the midrange. it's a honda cb350 twin
with stock
(CV?) keihin carbs and k&n pods.
of course, the stock air filters are just paper elements with a metal
casing. and the exhaust consists of two seperate headers leading to two
seperate mufflers. no cross-over of exhaust gases at all.

OK, so you have a twin cylinder machine with separate pipes and that is
a major clue
as to why you don't have the dreaded inline four flat spot.

The original poster has a motorcycle with an inline four cylinder
engine.

New riders who own inline fours often wonder why they have all those
carburetors, and, wouldn't it be simpler to just have ONE carburetor on
a simple log type manifold,
like a car has. That's why he asked about motorcycles that had single
carbs.

As I explained previously, George Kerker and other motorcycle
hotrodders decided to try 4-into-1 exhaust headers on the most popular
inline fours to take advantage of the high RPM cylinder over-filling
effect caused by another cylinder which is exhausting burnt mixture.

This effect can only work if the cylinder that is filling has valve
overlap. The intake valve opens early and the exhaust valve closes late
and a cylinder that is on the exhaust stroke helps suck fresh mixture
into the charging cylinder.

Problem is that the beneficial pressure waves in the exhaust system can
be out of phase with what you hope to accomplish. The speed of sound in
a gas is based upon its temperature and the exhaust system has a
certain tuned length and the pressure waves return to the cylinder at
regular intervals that can be determined by mathematical formulae.

The waves have to be "in synch" with the motions of the pistons. A
4-into-1 pipe returns a beneficial sucking wave at high RPM but it also
sends an adverse positive pressure wave back through the cylinder and
out the open intake valve and through the carburetor at some RPM.

The carb is a dumb device, it has no idea of which way the air is going
through it. So it picks up a shot of gasoline out of the float bowl and
throws it into the open air behind the carb, or into the air filter or
into the air box, depending on what you have.

Then the airflow reverses direction, the carburetor picks up a second
shot of gasoline.

The amateur tuner feels this problem as a flat spot between 5000 and
7000 to 8000 RPM, and imagine he might be able to do *something* with
jets, but it's a mystery. Nothing he does with jets works.

The various aftermarket exhaust system manufacturers offered pipes with
extra chambers to add volume, they offered 4-into-2-into-1 pipes and
claimed that they were the solution to the adverse pressure
wave-induced flat spot.

Some inventors even suggested variable length 4-into-1 pipes with
computer-controlled servo motors to vary the lengthof the system in
order to get rid of the flat spot.

But the system that works is Yamaha's ExUP, the computer-controlled
servo-operated exhaust throttling system. All of the Japan Inc.
manufacturers have adopted the ExUP system, with various acronyms that
seem to indicate that they invented it themselves.

The Older Gentleman

2006-06-13 17:58:53 UTC

Post by FB
OK, so you have a twin cylinder machine with separate pipes and that is
a major clue
as to why you don't have the dreaded inline four flat spot.

Um, just a question:

How come the manufacturers manage to produce in-line fours with
four-into-one pipes, without flat spots? I remember a very respected
tuner saying that the one huge mistake to make was that the factory
designer knew nothing about exhaust systems...

That said, a lot of aftermarket four-into-ones have been utterly
dreadful.

<snip>

Post by FB
But the system that works is Yamaha's ExUP, the computer-controlled
servo-operated exhaust throttling system. All of the Japan Inc.
manufacturers have adopted the ExUP system, with various acronyms that
seem to indicate that they invented it themselves.

Actually, no, they haven't, because Yamaha's patent lawyers would have
their arses if they did.

They have variations on a theme, agreed, but Yamaha's EXUP is indeed the
original and best. As was its YPVS system on its two-strokes. Yes, other
makers built power valves, but none was as elegant and effective as
Yamaha's, and nobody copied it for exactly the same reason they haven't
copied the EXUP. Patents.

"Yamaha's EXUP system that functions to eliminate torque valleys and
provide excellent power development characteristics has been made more
compact on this model while retaining the same basic operating
principle. Unlike the former system that included a separate valve for
each of the four exhaust pipes, the system on the new YZF-R1 places just
two EXUP valves at the points where the four exhaust pipes merge into
two, thus creating a more compact system that controls the pulse based
on calculations of the 1st and 2nd cylinders' exhaust and the 3rd and
4th cylinders' exhaust."

(From Yamaha's website)

And it's not just fitted to four-cylinder engines, either. *Please* stop
relying on your own perceived wisdom.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-13 20:04:05 UTC

Post by The Older Gentleman
How come the manufacturers manage to produce in-line fours with
four-into-one pipes, without flat spots? I remember a very respected
tuner saying that the one huge mistake to make was that the factory
designer knew nothing about exhaust systems...

You can use zero overlap valve timing.

Post by The Older Gentleman
That said, a lot of aftermarket four-into-ones have been utterly
dreadful.

Snip a bunch of cut and paste...

Post by The Older Gentleman
And it's not just fitted to four-cylinder engines, either. *Please* stop
relying on your own perceived wisdom.

Why? In a desert of one-liners and other egotistical post, my own
perceived wisdom is what I have to offer people who ask honest
questions.

If you will pardon me now, I shall go and assist the happy campers at
the lake...

The Older Gentleman

2006-06-14 06:21:23 UTC

Post by FB
Why? In a desert of one-liners and other egotistical post, my own
perceived wisdom is what I have to offer people who ask honest
questions.

Fine. As long as they get accurate answers....

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Ted Mittelstaedt

2006-06-14 04:45:50 UTC

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

What kind of motorcycle is it?

I've posted this before in this forum, but for the record it's a 1980 CB750K

Post by FB
Is it an inline-4?

Yes

Post by FB
Does it have a
4-into-1 pipe? Or does it have a stock exhaust system with balance
tubes between the pairs of exhaust pipes?

stock, 4 into 4.

Post by FB
Do you only ride in straight
lines, with no slow corners?

Only when I'm on the freeway (every day)

Seriously, I think your putting way too much reliance on any Hemholtz
resonance in the airbox fixing a flat spot. I have no doubt that
the airbox changes things, but I don't think it's as important as jetting
and general maintainence of the motorcycle - at least, not on a larger
displacement bike. Perhaps a 50-100 cc engine it would matter,
or perhaps if your racing at high speed (not some offroad dirt bike
thing) you would see a difference.

On my bike, the pod filters were on it when I bought the bike. I did
get the airbox from the prior owner, unfortunately it's missing one of
the manifold rubber connectors so it's just sitting until I can find a
replacement that won't break the bank.

Incidentally, there WAS a flat spot at 6000 RPM when I bought my
bike, in fact the seller commented on it. I thought it was carb settings
but I haven't yet got around to doing anything about the carbs. Do you
know what fixed it? I'll tell you. Replacing the chain.

When I bought my bike the chain was an old o-ring chain stretched to
the limit, most rings had fallen out of it, it was rusted, the front and
rear
sprockets were both pretty worn. I ran about 400 miles on that mess then
replaced everything, a new steel front sprocket, new aluminum rear sprocket,
and new O-ring chain. I did NOT change number of teeth on either sprocket,
and took pains to make sure that the sprockets had the same number of
teeth as the factory stock sprockets (the existing ones did, and the new
ones
do) In fact, seat-of-the-pants performance of the bike increased after
doing this.

My assumption is that the old chain and sprockets were so incredibly
worn and also adjusted too tight, that they somehow introduced enough
drag at speed as to create the flat spot. Beyond that I have no other
explanation, and I really don't like that explanation anyway, because
if the chain could have actually taken that much horsepower, why didn't it
break, or melt into slag.

Ted

2006-06-14 17:51:59 UTC

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

What kind of motorcycle is it?

I've posted this before in this forum, but for the record it's a 1980 CB750K

Well, I don't try to remember what every user in this NG rides or owns
or claims to have ridden or owned. The main idea of
rec.motorcycles.tech is that a newbie asks a question and we respond to
*that* question, avoiding turning the question into a debate.

Post by FB
Does it have a
4-into-1 pipe? Or does it have a stock exhaust system with balance
tubes between the pairs of exhaust pipes?

stock, 4 into 4.

Post by FB
Do you only ride in straight
lines, with no slow corners?

Only when I'm on the freeway (every day)

OK, that's what it is. You don't notice the flat spot when riding
straight up in a straight line because you can accelerate rapidly
through the RPM zone where reverse flow occurs.

Post by Ted Mittelstaedt
Seriously, I think your putting way too much reliance on any Hemholtz
resonance in the airbox fixing a flat spot. I have no doubt that
the airbox changes things, but I don't think it's as important as jetting
and general maintainence of the motorcycle - at least, not on a larger
displacement bike. Perhaps a 50-100 cc engine it would matter,
or perhaps if your racing at high speed (not some offroad dirt bike
thing) you would see a difference.

Racers routinely removed airboxes from their motorcycles in the early
1980's and replaced them with K&N's or foam Pods. The early 80's was an
era when drag racing
fascinated grass roots riders who weren't all that keen on going around
corners.

But, when the production racers like GSXR's became available the focus
changed to going around tight corners at part throttle and accelerating
out of the corners.

The racers began putting their airboxes back onto their bikes and
pretty soon they were also ducting cold air into the boxes and putting
ram air scoops on the fairings.

The ram air system may only give about 1/3rd of a pound of pressure,
but the extra density of the cooler air, combined with the resonant
frequency of the airbox helps to flatten out the midrange torque
valley.

The Older Gentleman

2006-06-14 19:59:16 UTC

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use individual pod air
filters, not an airbox?

What kind of motorcycle is it?

I've posted this before in this forum, but for the record it's a 1980 CB750K

Post by FB
Does it have a
4-into-1 pipe? Or does it have a stock exhaust system with balance
tubes between the pairs of exhaust pipes?

stock, 4 into 4.

Post by FB
Do you only ride in straight
lines, with no slow corners?

Only when I'm on the freeway (every day)

OK, that's what it is. You don't notice the flat spot when riding
straight up in a straight line because you can accelerate rapidly
through the RPM zone where reverse flow occurs.

Racers routinely removed airboxes from their motorcycles in the early
1980's and replaced them with K&N's or foam Pods. The early 80's was an
era when drag racing
fascinated grass roots riders who weren't all that keen on going around
corners.
But, when the production racers like GSXR's became available the focus
changed to going around tight corners at part throttle and accelerating
out of the corners.
The racers began putting their airboxes back onto their bikes and
pretty soon they were also ducting cold air into the boxes and putting
ram air scoops on the fairings.
The ram air system may only give about 1/3rd of a pound of pressure,
but the extra density of the cooler air, combined with the resonant
frequency of the airbox helps to flatten out the midrange torque
valley.

I had to X-post this to ukrm, where there are plenty of People WK.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Grimly Curmudgeon

2006-06-14 20:24:39 UTC

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember

Post by FB
The ram air system may only give about 1/3rd of a pound of pressure,
but the extra density of the cooler air, combined with the resonant
frequency of the airbox helps to flatten out the midrange torque
valley.

I had to X-post this to ukrm, where there are plenty of People WK.

Individual foam filters are only of any use in a custom mode - where you
don't or can't get a suitable airbox into the space available. In that
case they provide a cheap and easy fix with suitable jetting. Some
numbnuts run with only trumpet intakes and stone guards, but they're,
quite frankly, off their heads.

The manufacturers' airbox is a thing of beauty, designed to flow
sufficient air at all parts of the rev range and avoid such problems as
mentioned above, such as flat spots, etc. If you had to pay for an
airbox solution and somebody was selling the same, you could bet your
arse that airboxes would be the next cool thing.

You get them for free with most bikes and they do the job they're
supposed to do. People who throw airboxes away are idiots.

--
Dave
GS850x2 XS650 SE6a
Teeth of the Jungle.
***@Home Team UKRM http://www.tinyurl.com/jkxwv

ChrisDC

2006-06-14 20:51:16 UTC

On Wed, 14 Jun 2006 21:24:39 +0100, Grimly Curmudgeon

Post by Grimly Curmudgeon
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember

I had to X-post this to ukrm, where there are plenty of People WK.

Individual foam filters are only of any use in a custom mode - where you
don't or can't get a suitable airbox into the space available. In that
case they provide a cheap and easy fix with suitable jetting. Some
numbnuts run with only trumpet intakes and stone guards, but they're,
quite frankly, off their heads.
The manufacturers' airbox is a thing of beauty, designed to flow
sufficient air at all parts of the rev range and avoid such problems as
mentioned above, such as flat spots, etc. If you had to pay for an
airbox solution and somebody was selling the same, you could bet your
arse that airboxes would be the next cool thing.
You get them for free with most bikes and they do the job they're
supposed to do. People who throw airboxes away are idiots.

Maybe, but I used to have all the dyno graphs from the work on my
XJ900F, done at Dynojet's place in Warrington. They borrowed my bike
to develop their stage 1 and stage 3 kits for the XJ, and did 30 - 40
dyno runs in all.

At stage 3 it had individual K&Ns and a Laser race 4-2 exhaust plus
the appropriate Dynojet kit.

The torque curves were beautifully flat, with no holes at all, and the
power was up by 12% on stock over most of the range and rather more
where it had filled in the mid-range dip.

--
Chris
VN1500-j1 (Gertrude) Twice the fun at half the speed.
chris.desclayes at ffcc dot powernet dot co dot uk
But minus one "f"

2006-06-14 21:01:27 UTC

Post by ChrisDC
The torque curves were beautifully flat, with no holes at all, and the
power was up by 12% on stock over most of the range and rather more
where it had filled in the mid-range dip.

Yebbut, midrange dips were designed into engines to get through noise
regs... weren't they?

--
Mike
FJ1200

ChrisDC

2006-06-14 21:27:25 UTC

Post by mb

Post by ChrisDC
The torque curves were beautifully flat, with no holes at all, and the
power was up by 12% on stock over most of the range and rather more
where it had filled in the mid-range dip.

Yebbut, midrange dips were designed into engines to get through noise
regs... weren't they?

So I believe. The race cans made that irrelevant.

--
Chris
VN1500-j1 (Gertrude) Twice the fun at half the speed.
chris.desclayes at ffcc dot powernet dot co dot uk
But minus one "f"

2006-06-15 02:01:03 UTC

Post by ChrisDC
Maybe, but I used to have all the dyno graphs from the work on my
XJ900F, done at Dynojet's place in Warrington. They borrowed my bike
to develop their stage 1 and stage 3 kits for the XJ, and did 30 - 40
dyno runs in all.
At stage 3 it had individual K&Ns and a Laser race 4-2 exhaust plus
the appropriate Dynojet kit.
The torque curves were beautifully flat, with no holes at all, and the
power was up by 12% on stock over most of the range and rather more
where it had filled in the mid-range dip.

Hello? Dyno runs are NOT representative of real world riding
conditions. If you have an inertia dyno and you rev up the engine and
get a run at the rollers, you shoot right through the flat spot with no
problems, just like drag racing or straight line street runs.

You need an complete engine tuning package for road racing that lets
the engine pull its way out of the torque valley when it's stuck down
there in a slow corner and you're between optimum gears.

Some modern engines have specially treated connecting rods to allow
over-revving in 2nd gear to avoid shifting up and down in medium speed
corners. Every extra shift wastes about 1/2 a second and that counts
when you're trying to get your lap times down.

The Older Gentleman

2006-06-15 06:18:59 UTC

Post by FB
Some modern engines have specially treated connecting rods to allow
over-revving in 2nd gear

Now that I didn't know.

They do? Which ones?

And why should over-revving in second gear be any different from
over-revving in any other gear?

You sure you're not confusing this with the little electronic gizmos
that prevent over-revving so you don't wheelie the eff out of it in
first and second?

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-15 16:05:47 UTC

Post by FB
Some modern engines have specially treated connecting rods to allow
over-revving in 2nd gear

Now that I didn't know.
They do? Which ones?

You are welcome to use my knowledge of the history of high performance
engines in one of your free lance articles. Don't be shy about it. It's
all been published before.

Ask Kevin Cameron. He knows.

Piston ring flutter was the problem that limited upper RPM limits until
Honda came out with ultra thin low mass piston rings in the 1960's.
Wiseco jumped onto the thin rings and made thin ring pistons for the
general public's Yamaha 250's in the mid-1960's. Now thin ring pistons
are in all the high performance machines.

Then the problem was connecting rod breakage at around 13K RPM. Suzuki
solved that problem with expen$ive Carillo I-beam con rods. But, at
$1000 a set, a
street bike/box stock racer wouldn't be regarded as such a bargain,
they wouldn't fly off the show room floors if they cost $5000 instead
of $4000.

Though the Yoshimura GXSR-750 that was first seen in 1985 had a 13K red
line with
about 130 horsepower, the GSXR that Americans received was
electronically limited to a peak of only 11K RPM and riders were lucky
to get 80 or 90 horsepower out of it.

So Suzuki found a way to upgrade the rods inexpensively in the early
1990's.

It's probably the same process that Yamaha used on the 600cc R6,
carburizing or flame hardening the surface to a shallow depth.

In the theory of strength of materials, loads are carried on or near
the surfaces of the structural members, so surface hardening makes
sense in theory and seems to work in practice.

Now that the piston ring and connecting rod problems are solved, the
issue that limits
engine life is cracking around the piston's wrist pin bosses, according
to K. Cameron.

Post by The Older Gentleman
And why should over-revving in second gear be any different from
over-revving in any other gear?

Most gear boxes have a first gear spaced much further apart than the
other 4 or 5 gears. There is like a 30% RPM drop shifting from 1st to
2nd gears, then a 15% drop between 2nd and 3rd, etc.

By the same token, shifting down from 2nd into 1st increases the RPM by
30% and the rider has a hard time controlling the throttle and traction
when the crankshaft flywheels may suddenly slow the machine down. First
gear is generally unusable in a slow corner because of crankshaft
inertia slowing the machine too much.

Norton Manxes needed a really tall 1st gear in their 4-speed
transmissions in order to be usable on a race track and they were tuned
to run "on the horn" with the intake horn and exhaust megaphone working
together at a critical RPM.

The rider had to stay "on the horn" by slipping the clutch in slow
corners and when first leaving the starting line at the beginning of
the race.

Honda tried increasing the number of gearbox ratios so their peaky
tuned engines would always have a gear available that the rider could
select to keep things perking inside the buzzy little engines. The FIM
outlawed excess gear sets, so the only thing left was ridiculously tall
first gears, or over-revving the engine past the torque peak in a lower
gear to avoid shifting.

On many GP and AMA national road race courses, the motorcycles will be
running in either 2nd or 3rd gear through most corners, and revving
past the torque peak to avoid upsetting the chassis when shifting gears
with the machine leaned over.

You can see what gear the motorcycle is in and what RPM and speed the
motorcycle is going in a box at the top of the screen. The world
champion and national class champions are only in 4th, 5th and 6th
gears on the longest straights.

Post by The Older Gentleman
You sure you're not confusing this with the little electronic gizmos
that prevent over-revving so you don't wheelie the eff out of it in
first and second?

Nope. There are RPM limiting or ignition advance limiting circuits on
some machines, but the riders over rev their engines in the lower gears
to avoid shifting while leaned over.

Champ

2006-06-15 17:20:43 UTC

Post by FB
Some modern engines have specially treated connecting rods to allow
over-revving in 2nd gear

Now that I didn't know.
They do? Which ones?

You are welcome to use my knowledge of the history of high performance
engines in one of your free lance articles. Don't be shy about it. It's
all been published before.
Ask Kevin Cameron. He knows.

<mega snip>

Sure, sure - everything you've just trotted out is standard stuff.
The point remains that you can't "specially treat a conrod to allow
over-rev in 2nd gear". If you treat the rod to allow higher revs (due
to a higher mean piston speed), then that's going to apply to every
gear, so why not use it in every gear.

Most of what you say about the gap between 1st and 2nd gear isn't
really applicable to race machines, or even modern sports machines -
my current ZX10R pulls to 105mph in first, which makes first very
usable for 40~50mph corners.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

2006-06-15 19:54:15 UTC

Post by Champ
Sure, sure - everything you've just trotted out is standard stuff.
The point remains that you can't "specially treat a conrod to allow
over-rev in 2nd gear".

If you play with your brain too much, you'll go insane.

The Older Gentleman

2006-06-15 18:33:02 UTC

FB <***@yahoo.com> wrote:

<snip>

Post by FB
So Suzuki found a way to upgrade the rods inexpensively in the early
1990's.

Yes, yes, yes.

I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-15 19:57:08 UTC

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

I don't have time to teach you about acceleration loads, I have to go
and help the happy campers at the lake. And, besides, it's already
happy hour over there and your brain is probably already well-impaired.

Bear

2006-06-15 20:01:12 UTC

On 15 Jun 2006 12:57:08 -0700, FB said ...

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

Can I have a guess?

Is it because the back load on the gearbox sprocket (and thus rest of
the drive chain) is at its highest, in relation to the power put through
it, on the limit in second?

If by a 1,000,000 to 1 chance I'm actually right the world as we know it
will cease to exist in a puff of illogic, so let's pray I'm wrong as
usual.

--
Bear

Champ

2006-06-15 20:41:14 UTC

Post by Bear
On 15 Jun 2006 12:57:08 -0700, FB said ...

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

Can I have a guess?
Is it because the back load on the gearbox sprocket (and thus rest of
the drive chain) is at its highest, in relation to the power put through
it, on the limit in second?

I'm unconvinced. I think the highest load is usually when in the
highest gear. It's certainly when the boost gauges on turbo motors
show the highest boost, demonstrating that the engine is flowing the
most gas.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Bear

2006-06-15 20:50:29 UTC

On Thu, 15 Jun 2006 21:41:14 +0100, Champ said ...

Post by Bear
On 15 Jun 2006 12:57:08 -0700, FB said ...

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

Can I have a guess?
Is it because the back load on the gearbox sprocket (and thus rest of
the drive chain) is at its highest, in relation to the power put through
it, on the limit in second?

I wasn't talking about peak gas flow, or peak power, I was talking about
peak back load as it relates to power output.

I'll wait for his answer. There's a reason I replied, mechanical numpty
though I am.

--
Bear

The Older Gentleman

2006-06-15 21:04:06 UTC

Post by Bear
On 15 Jun 2006 12:57:08 -0700, FB said ...

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

Can I have a guess?
Is it because the back load on the gearbox sprocket (and thus rest of
the drive chain) is at its highest, in relation to the power put through
it, on the limit in second?
If by a 1,000,000 to 1 chance I'm actually right the world as we know it
will cease to exist in a puff of illogic, so let's pray I'm wrong as
usual.

Interesting point. I dunno. I just can't believe that conrods are
strengthened purely because of second gear. Sorry. Load is load.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

The Older Gentleman

2006-06-15 21:04:06 UTC

Post by The Older Gentleman
I really don't know how to make you understand that strengthening
conrods is something that is of benefit in *any* gear, not just second.

OK, enlighten me. A bike will accelerate faster in in first than in
second....

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Champ

2006-06-14 22:09:51 UTC

On Wed, 14 Jun 2006 21:24:39 +0100, Grimly Curmudgeon

Post by Grimly Curmudgeon
Individual foam filters are only of any use in a custom mode - where you
don't or can't get a suitable airbox into the space available. In that
case they provide a cheap and easy fix with suitable jetting. Some
numbnuts run with only trumpet intakes and stone guards, but they're,
quite frankly, off their heads.

Have you seen Sweller's guzzi?

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Wicked Uncle Nigel

2006-06-14 22:56:08 UTC

Using the patented Mavis Beacon "Hunt&Peck" Technique, Champ

Post by ChrisDC
On Wed, 14 Jun 2006 21:24:39 +0100, Grimly Curmudgeon

Have you seen Sweller's guzzi?

And this negates the "off their heads" assertion how, exactly?

--
Wicked Uncle Nigel - Podium Placed Ducati Race Engineer

WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
SBS#39 OMF#6 Enfield 500 Curry House Racer "The Basmati Rice Burner",
Honda GL1000K2 (On its hols) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
Suzuki TS250 "The Africa Single" Yamaha GTS1000 Honda ST1100 wiv trailer

Champ

2006-06-14 22:59:04 UTC

On Wed, 14 Jun 2006 23:56:08 +0100, Wicked Uncle Nigel

Post by Wicked Uncle Nigel
Using the patented Mavis Beacon "Hunt&Peck" Technique, Champ

Post by ChrisDC
On Wed, 14 Jun 2006 21:24:39 +0100, Grimly Curmudgeon

Have you seen Sweller's guzzi?

And this negates the "off their heads" assertion how, exactly?

Ah. Yes. Good point.

But at least he's not off his head in any engineering sense.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Grimly Curmudgeon

2006-06-14 23:14:29 UTC

We were somewhere around Barstow, on the edge of the desert, when the

Post by Wicked Uncle Nigel

Post by Champ
Have you seen Sweller's guzzi?

And this negates the "off their heads" assertion how, exactly?

Ah. Yes. Good point.
But at least he's not off his head in any engineering sense.

I'd rather have a K&N than nothing at all. The shite that gets sucked in
will cause bore and piston wear.

--
Dave
GS850x2 XS650 SE6a
Teeth of the Jungle.
***@Home Team UKRM http://www.tinyurl.com/jkxwv

sweller

2006-06-15 06:14:29 UTC

Post by Wicked Uncle Nigel

Some numbnuts run with only trumpet intakes and
stone guards, but they're, quite frankly, off their heads.

Have you seen Sweller's guzzi?

And this negates the "off their heads" assertion how, exactly?

Ah. Yes. Good point.
But at least he's not off his head in any engineering sense.

It does have gauze and paper K&Ns. They're a bit battered and really
need replacing.

--
Simon

Grimly Curmudgeon

2006-06-15 15:52:32 UTC

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "sweller"

Post by sweller
It does have gauze and paper K&Ns. They're a bit battered and really
need replacing.

Somehow I doubted you were mad enough to have only trumpets.

--
Dave
GS850x2 XS650 SE6a
Teeth of the Jungle.
***@Home Team UKRM http://www.tinyurl.com/jkxwv

Grimly Curmudgeon

2006-06-14 23:13:13 UTC

We were somewhere around Barstow, on the edge of the desert, when the

Post by Champ
Some

Post by Grimly Curmudgeon
numbnuts run with only trumpet intakes and stone guards, but they're,
quite frankly, off their heads.

Have you seen Sweller's guzzi?

Got trumpets?

--
Dave
GS850x2 XS650 SE6a
Teeth of the Jungle.
***@Home Team UKRM http://www.tinyurl.com/jkxwv

Pete Fisher

2006-06-14 20:10:20 UTC

In message

Post by Ted Mittelstaedt
Why doesen't my bike have a midrange flat spot, I use
individual pod air
filters, not an airbox?

What kind of motorcycle is it?

I've posted this before in this forum, but for the record it's a 1980 CB750K

Post by FB
Does it have a
4-into-1 pipe? Or does it have a stock exhaust system with balance
tubes between the pairs of exhaust pipes?

stock, 4 into 4.

Post by FB
Do you only ride in straight
lines, with no slow corners?

Only when I'm on the freeway (every day)

OK, that's what it is. You don't notice the flat spot when riding
straight up in a straight line because you can accelerate rapidly
through the RPM zone where reverse flow occurs.

Racers routinely removed airboxes from their motorcycles in the early
1980's and replaced them with K&N's or foam Pods. The early 80's was an
era when drag racing
fascinated grass roots riders who weren't all that keen on going around
corners.
But, when the production racers like GSXR's became available the focus
changed to going around tight corners at part throttle and accelerating
out of the corners.
The racers began putting their airboxes back onto their bikes and
pretty soon they were also ducting cold air into the boxes and putting
ram air scoops on the fairings.
The ram air system may only give about 1/3rd of a pound of pressure,
but the extra density of the cooler air, combined with the resonant
frequency of the airbox helps to flatten out the midrange torque
valley.

I had to X-post this to ukrm, where there are plenty of People WK.

People Who Kayak ?

I will thumb through my ancient dog eared 'Tuning for Speed' to see if
Saint Phil has anything to say on the subject, but as it was written in
the days of 7Rs (that's PROPER ONES CHAMP) and Vincents he may be silent
on the matter.

--
+-----------------------------------------------------------------+
| Pete Fisher at Home: ***@ps-fisher.demon.co.uk |
| Voxan Roadster Moto Guzzi Mille GT/Squire RS3 Gilera Nordwest |
| Gilera GFR Moto Morini 2C/375 |
+-----------------------------------------------------------------+

Champ

2006-06-14 22:09:06 UTC

On Wed, 14 Jun 2006 21:10:20 +0100, Pete Fisher

Post by Pete Fisher
I will thumb through my ancient dog eared 'Tuning for Speed' to see if
Saint Phil has anything to say on the subject, but as it was written in
the days of 7Rs (that's PROPER ONES CHAMP) and Vincents he may be silent
on the matter.

heh. And G50s too, no doubt.

PS learn to snip, newbie.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Pete Fisher

2006-06-14 22:20:11 UTC

Post by Champ
PS learn to snip, newbie.

<suitably chastised>
Oops. Tired and emotional at time of posting. All misty eyed after
blowing the dust of TFS and opening it to find all my old gear ratio
calcs from the two stroke single class road racing days.

2006-06-15 02:04:40 UTC

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

The newbie question has been asked and answered.

The original poster said he was quite satisfied with my explanation of
why motorcycles have multiple carbs instead of one carb on a manifold.

muddy

2006-06-15 02:39:33 UTC

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

Because you replied to it YTC.

--
Mike
DL1000 Combat Touring Special
UKRMMA#22

The Older Gentleman

2006-06-15 06:18:59 UTC

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?
The newbie question has been asked and answered.
The original poster said he was quite satisfied with my explanation of
why motorcycles have multiple carbs instead of one carb on a manifold.

Because the rest of your assertion was questionable?

Specifically, this onbe:

"OK, so you have a twin cylinder machine with separate pipes and that is
a major clue as to why you don't have the dreaded inline four flat
spot."

You're saying that four-into-one exhausts have flat spots, and I rather
disagree with that.

You also said that only Yamaha's EXUP solves the problem. Also
questionable.

You also said that other Jap manufacturers have copied Yamaha's EXUP
system, and I pointed out that Yamaha's patent lawyers prevent them from
doing so. Other makers have their own variations on the theme, but the
EXUP is an original. You snipped that bit.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Simon Gates

2006-06-15 09:02:23 UTC

Post by The Older Gentleman
You also said that other Jap manufacturers have copied Yamaha's EXUP
system, and I pointed out that Yamaha's patent lawyers prevent them from
doing so. Other makers have their own variations on the theme, but the
EXUP is an original. You snipped that bit.

The first EXUP was released in '89, wasn't it? The patent will have run
out at the latest this year, and more likely 2003-ish.

Eiron

2006-06-15 19:10:23 UTC

Post by Simon Gates

The first EXUP was released in '89, wasn't it? The patent will have run
out at the latest this year, and more likely 2003-ish.

I saw an old British single in the seventies with a butterfly valve between the
header and the megaphone. It was open at high engine speeds for power and shut
at low engine speeds or when passing PC Plod, if the rider remembered in time.

--
Eiron

No good deed ever goes unpunished.

The Older Gentleman

2006-06-15 21:04:07 UTC

Post by Eiron
I saw an old British single in the seventies with a butterfly valve
between the header and the megaphone. It was open at high engine speeds
for power and shut at low engine speeds or when passing PC Plod, if the
rider remembered in time.

Someone in the 1970s made an exhaust with a baffle-onna-pivot and a
cable control, so you could open or close it at will. More for noise
than anything else. Wish I could remember who made it.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

platypus

2006-06-15 21:19:43 UTC

Post by Eiron
I saw an old British single in the seventies with a butterfly valve
between the header and the megaphone. It was open at high engine
speeds for power and shut at low engine speeds or when passing PC
Plod, if the rider remembered in time.

Someone in the 1970s made an exhaust with a baffle-onna-pivot and a
cable control, so you could open or close it at will. More for noise
than anything else. Wish I could remember who made it.

Alistair Laurie, who used to produce gorgeous Trident specials, would fit a
sort of butterfly valve in his exhausts.

--
platypus

and there's nothing I can do

The Older Gentleman

2006-06-15 21:34:21 UTC

Post by platypus

Post by Eiron
I saw an old British single in the seventies with a butterfly valve
between the header and the megaphone. It was open at high engine
speeds for power and shut at low engine speeds or when passing PC
Plod, if the rider remembered in time.

Someone in the 1970s made an exhaust with a baffle-onna-pivot and a
cable control, so you could open or close it at will. More for noise
than anything else. Wish I could remember who made it.

Alistair Laurie, who used to produce gorgeous Trident specials, would fit a
sort of butterfly valve in his exhausts.

Could have been him. Didn't he also make amazing Laverda specials?
Elizabeth's Taxi comes to mind.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Champ

2006-06-15 11:21:10 UTC

On Thu, 15 Jun 2006 07:18:59 +0100,

I don't think this is actually true. As Simon says, I thought the
patent had expired, which is why the other manufacturers all had EXUP
style systems now.

--
Champ

ZX10R
GPz750turbo

chateau.murray@btinternet.com,

2006-06-15 11:25:31 UTC

Post by Champ
On Thu, 15 Jun 2006 07:18:59 +0100,

I don't think this is actually true. As Simon says, I thought the
patent had expired, which is why the other manufacturers all had EXUP
style systems now.

If that's the case, I stand corrected.

Bear

2006-06-15 13:20:16 UTC

On Thu, 15 Jun 2006 12:21:10 +0100, Champ said ...

Post by Champ
On Thu, 15 Jun 2006 07:18:59 +0100,

I don't think this is actually true. As Simon says, I thought the
patent had expired, which is why the other manufacturers all had EXUP
style systems now.

Indeed so.

--
Bear

chateau.murray@btinternet.com,

2006-06-15 14:12:22 UTC

Post by Bear
On Thu, 15 Jun 2006 12:21:10 +0100, Champ said ...

Post by Champ
On Thu, 15 Jun 2006 07:18:59 +0100,

I don't think this is actually true. As Simon says, I thought the
patent had expired, which is why the other manufacturers all had EXUP
style systems now.

Indeed so.

Indeed so. Apologies.

Bob Myers

2006-06-15 18:32:54 UTC

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

OK, let's end it right now.

The reason that there is 1 carb per cylinder is that two or three
would be silly.

There, now we can all happily go back to our lives....move
along, folks, nothing left here to see....

Bob M.

Post by FB
The newbie question has been asked and answered.
The original poster said he was quite satisfied with my explanation of
why motorcycles have multiple carbs instead of one carb on a manifold.

The Older Gentleman

2006-06-15 18:36:12 UTC

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Champ

2006-06-15 18:50:01 UTC

On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

ogden

2006-06-15 18:57:36 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

That's nothing. They built a v8 with four cylinders.

--
ogden

Bear

2006-06-15 19:32:38 UTC

On Thu, 15 Jun 2006 19:50:01 +0100, Champ said ...

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha certainly did.

--
Bear

Champ

2006-06-15 20:41:40 UTC

Post by Bear
On Thu, 15 Jun 2006 19:50:01 +0100, Champ said ...

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha certainly did.

That's the badger.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

ginge

2006-06-15 19:35:47 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

I don't know about honda, but the SZR660 in my garage has 2 carbs, 1
cylinder, and 5 valves.

The Older Gentleman

2006-06-15 21:04:07 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Bob Myers

2006-06-15 21:39:35 UTC

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Fine. Go ahead and spoil a perfectly good joke. Would
you have been happier had I said "three or four"?

Bob M.

Champ

2006-06-15 22:05:11 UTC

On Thu, 15 Jun 2006 21:39:35 GMT, "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Fine. Go ahead and spoil a perfectly good joke.

It's a shame, isn't it. One has to be eternally vigilant round here,
y'know.

Post by Bob Myers
Would you have been happier had I said "three or four"?

That would have spoilt our fun.

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Verdigris

2006-06-15 21:19:17 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Is there actually an advantage to two carbs, rather than one big one?

--
Simon - UKRM~verdigris,plus,com
Tiger - A return to good sense.
Z1000 - Less sense, more sensation.
MAG BOTAFOT#36 two#22 HLR#pi BONY#62 BHaLC#3 LotR#7

WavyDavy(Mobile)

2006-06-15 21:57:38 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Is there actually an advantage to two carbs, rather than one big one?

The velocity of the air over each needle in a (small) two carb set-up
should, I think, be faster than the velocity of air over the needle in a
(large) single carb, thus making a more responsive/efficient engine. Its a
bit similar to why big twins (think 916 through 999, Tl-series and SP1/2
plus others) use injection over carbs - to flow enough air at high revs in a
large cylinder, the carbs have to be so big that, at low revs they're
shit.... Use two small carbs and that makes up the carbs opening surface
area at high revs whilst keeping the fast airflow of smaller carbs for low
revs.

Or something

Dave

Bear

2006-06-15 21:59:50 UTC

On Thu, 15 Jun 2006 22:19:17 +0100, Verdigris said ...

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Is there actually an advantage to two carbs, rather than one big one?

IIRC the output of a single carb, mixture-wise, is largely (but not
exclusively) linear, whereas a twin carb setup produces an amount of
combustable vapour that rises almost exponentially, as first one, then
the other carb chimes in. Suited to big singles, which need next to no
mixture in their lower rev range, but a fair old whack in their upper
rev reaches.

BICBW.

--
Bear

Rick Cortese

2006-06-16 05:58:05 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Is there actually an advantage to two carbs, rather than one big one?

I know I should stay away but...

Sometimes

I kind of disagree with the other posters about what is the big reason
for this. The reason Honda used two carbs rather then one is because we
are talking about 2 intake valves per cylinder.

It is this simple: Air flow doesn't like turns. There's a lot of other
stuff air flow doesn't like, but turns is the big one here.

To see and extreme example of this you would have to look under the hood
of a NASCAR car. They are limited by rules to a single 4 barrel carb so
what they do is cut it in half and move the halves apart so they can
straighten out the intake runners.

The sometimes qualifier is because: Let's say your riding a motorcycle
with an engine about equal to one in a garden tractor. Chances are you
aren't going to see much benefit at your 1,800 RPM redline. Tiny valves,
mild cam, low RPM, all that kind of stuff negates the benefit/need of
straightening out the intake paths.

The Older Gentleman

2006-06-16 06:16:20 UTC

Post by Champ
On Thu, 15 Jun 2006 19:36:12 +0100,

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

<VVBG>

butbutbut - didn't Honda build a big single with two carbs at some
point?

Yamaha big singles have had two carbs for years.

Is there actually an advantage to two carbs, rather than one big one?

IIRC Yamaha's excuse is that the CV carb works for nice fine adjustment
lower down the rev range and the slide one is for banging in fuill chat
higher up.

Big singles are notoriously finicky things once you try and get any sort
of power out of them - Yamaha actually had to delay the launch of the
XT500 by a year because it was proving such a troublesome engine to
develop, and everything but everything was breaking in testing.

Mind you, it was only the second four-stroke lump they'd built, so they
can be forgiven.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Ace

2006-06-16 07:55:58 UTC

On Fri, 16 Jun 2006 07:16:20 +0100,

Post by The Older Gentleman
Big singles are notoriously finicky things once you try and get any sort
of power out of them - Yamaha actually had to delay the launch of the
XT500 by a year because it was proving such a troublesome engine to
develop, and everything but everything was breaking in testing.
Mind you, it was only the second four-stroke lump they'd built, so they
can be forgiven.

Eh? They'd made loads by then, shirley? I can think of three twins off
the top of my head: XS1/650, XS/TX500, TX750 (not UK). And I'm not
even sure that the XS750 triple didn't pre-date the XT motor, although
release dates might have been different in different markets.

--
_______
.'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

TOG@toil, chateau.murray@btinternet.com,

2006-06-16 08:18:07 UTC

Post by Ace
On Fri, 16 Jun 2006 07:16:20 +0100,

Yes, you're right. It went XS650, and then TX500/XS500 more or less
simultaneously with the TX750 (which we never got in the UK). The XT500
definitely pre-dated the XS750 triple, though.

Wicked Uncle Nigel

2006-06-15 18:56:25 UTC

Using the patented Mavis Beacon "Hunt&Peck" Technique, Bob Myers

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Agreed. V-Maxes are *very* silly.

Bear

2006-06-15 19:37:31 UTC

On Thu, 15 Jun 2006 19:56:25 +0100, Wicked Uncle Nigel said ...

Post by Wicked Uncle Nigel
Using the patented Mavis Beacon "Hunt&Peck" Technique, Bob Myers

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Agreed. V-Maxes are *very* silly.

Oooh that's stretching an engineering point just a *little* too far [1],
but well spotted.

[1] yeah ok, V-Boost does channel output from more than one carb into
one cylinder, but that's not what he meant and you know it :)

--
Bear

Wicked Uncle Nigel

2006-06-15 21:20:40 UTC

Using the patented Mavis Beacon "Hunt&Peck" Technique, Bear

Post by Bear
On Thu, 15 Jun 2006 19:56:25 +0100, Wicked Uncle Nigel said ...

Post by Wicked Uncle Nigel
Using the patented Mavis Beacon "Hunt&Peck" Technique, Bob Myers

Post by The Older Gentleman
I had to X-post this to ukrm, where there are plenty of People WK.

Why does this thread have to go on and on and on in
rec.motorocycles.tech?

OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Agreed. V-Maxes are *very* silly.

Oooh that's stretching an engineering point just a *little* too far [1],
but well spotted.
[1] yeah ok, V-Boost does channel output from more than one carb into
one cylinder, but that's not what he meant and you know it :)

I stand by my point.

And I still want one.

ChrisDC

2006-06-15 19:23:11 UTC

On Thu, 15 Jun 2006 18:32:54 GMT, "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Yamaha SRX.

1 cylinder, 2 carbs. And...

Dreadful warm start performance.

--
Chris
VN1500-j1 (Gertrude) Twice the fun at half the speed.
chris.desclayes at ffcc dot powernet dot co dot uk
But minus one "f"

Dr Zoidberg

2006-06-15 19:32:26 UTC

Post by ChrisDC
On Thu, 15 Jun 2006 18:32:54 GMT, "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Yamaha SRX.
1 cylinder, 2 carbs. And...

It was more like one and a half

Post by ChrisDC
Dreadful warm start performance.

Mine was ok , apart from when one of the rubber manifolds split

--
Alex

Piece by piece the penguins have taken my sanity
www.drzoidberg.co.uk www.ebayfaq.co.uk

Grimly Curmudgeon

2006-06-15 20:23:27 UTC

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Honda thingy err,, something or other, had a dual-choke carb feeding a
single cylinder. XL 500?

--
Dave
GS850x2 XS650 SE6a
Teeth of the Jungle.
***@Home Team UKRM http://www.tinyurl.com/jkxwv

Bob Myers

2006-06-15 21:43:42 UTC

Post by Grimly Curmudgeon
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Honda thingy err,, something or other, had a dual-choke carb feeding a
single cylinder. XL 500?

Y'see, this is precisely the problem with trying to inject any sort
of humor into a technical group. The moment you do, SOMEONE
is just bound to trot out the "well, yeah, but didn't Tappet Bros.
Motors, in their 1927 Feeblevitzer model, have an engine which
used a secondary Thelmann wire in the reverse-framistat
confabulator?"

Killjoys. Each 'n' every one o' ya.....

:-) :-) ;-)

Bob M.

Champ

2006-06-15 22:06:01 UTC

On Thu, 15 Jun 2006 21:43:42 GMT, "Bob Myers"

Post by Grimly Curmudgeon
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Bob Myers"

Post by Bob Myers
OK, let's end it right now.
The reason that there is 1 carb per cylinder is that two or three
would be silly.

Honda thingy err,, something or other, had a dual-choke carb feeding a
single cylinder. XL 500?

Wasn't that pioneered by Spagthorpe? Where's Grimley when you need
him?

--
Champ

ZX10R
GPz750turbo
My advice as your attorney is to buy a motorcycle

Ted Mittelstaedt

2006-06-15 08:26:09 UTC

Post by FB
Do you only ride in straight
lines, with no slow corners?

Only when I'm on the freeway (every day)

OK, that's what it is. You don't notice the flat spot when riding
straight up in a straight line because you can accelerate rapidly
through the RPM zone where reverse flow occurs.

The freeway doesen't come to my front door, I have to ride about 2 miles
north on a 35Mph road with many traffic lights to catch it. And several
times during the week I have to go to customer sites where the freeway
is only part of the way there.

Racers routinely removed airboxes from their motorcycles in the early
1980's and replaced them with K&N's or foam Pods. The early 80's was an
era when drag racing
fascinated grass roots riders who weren't all that keen on going around
corners.
But, when the production racers like GSXR's became available the focus
changed to going around tight corners at part throttle and accelerating
out of the corners.
The racers began putting their airboxes back onto their bikes and
pretty soon they were also ducting cold air into the boxes and putting
ram air scoops on the fairings.
The ram air system may only give about 1/3rd of a pound of pressure,
but the extra density of the cooler air, combined with the resonant
frequency of the airbox helps to flatten out the midrange torque
valley.

I think the operative word here is "helps" and you have to have a midrange
torque vally to begin with for airbox fun and games to make a difference.
For bikes that don't, the airbox does very little.

Ted

The Older Gentleman

2006-06-15 18:33:02 UTC

Post by Ted Mittelstaedt
I think the operative word here is "helps" and you have to have a midrange
torque vally to begin with for airbox fun and games to make a difference.
For bikes that don't, the airbox does very little.

This is true. The manufacturers have only really started optimising
airbox performance, and "tuning" them, in the last decade or two.

For older bikes, they were simply... well, a box to put the air filter
in.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Mark Olson

2006-06-15 21:15:59 UTC

This is true. The manufacturers have only really started optimising
airbox performance, and "tuning" them, in the last decade or two.
For older bikes, they were simply... well, a box to put the air filter
in.

The exhaust 'collector' on the '78 SR500E I've recently been fettling is
an obvious Helmholz resonator, and I'll wager the same bods that ginned
up the exhaust might have had a peek at the airbox as well.

--
'01 SV650S '99 EX250-F13 '98 ZG1000A-13 '81 CM400T
OMF #7

The Older Gentleman

2006-06-15 21:34:22 UTC

Post by Mark Olson

This is true. The manufacturers have only really started optimising
airbox performance, and "tuning" them, in the last decade or two.
For older bikes, they were simply... well, a box to put the air filter
in.

OK, granted. I remember my old SR too. My 400 Four, OTOH.......

Not to mention a long series of Honda twins. My 1978 CB200 had twin air
filters, one either sid eof the frame, and the filter boxes were
integral with the filter elements - they were just plastic covers.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Les

2006-06-12 17:14:10 UTC

Post by m***@merr.com
I'm an amateur just beginning to work on my own bikes (GS850L &
CB450) and I'm wondering if there are any multiple cylinder bikes
that operate with one carb like most cars do.? Thanks for any input

It is rather difficult to fit a single carb with an intake manifold on
a bike.

(And not for the first time he posts this reply...)
Complete and utter nonsense.

Cites please.
I would love to see someone put an intake maniford and a single carb on
something like a KZ-1300 and then tell me that it was easy.

Settle for a CSR-650 inline 4 when I start working on it? I'll more than
likely set it up with a single carb, just to be different.

The Older Gentleman

2006-06-12 17:45:25 UTC

Post by m***@merr.com
I'm an amateur just beginning to work on my own bikes (GS850L &
CB450) and I'm wondering if there are any multiple cylinder bikes
that operate with one carb like most cars do.? Thanks for any input

It is rather difficult to fit a single carb with an intake manifold on
a bike.

(And not for the first time he posts this reply...)
Complete and utter nonsense.

Cites please.
I would love to see someone put an intake maniford and a single carb on
something like a KZ-1300 and then tell me that it was easy.

Well, after I posted, I realised you were probably talking about fours,
but the OP referred also to a CB450 and they're twins.

As you know, just about every brit twin made for years had a single-carb
version. So did many Hondas.

Kawasaki Z1300s made two with three carbs before they went to FI.

But, agreed, I've never seen a four-cylinder bike with a single carb,
except possibly a Nimbus or Henderson.

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

James Clark

2006-06-13 03:49:12 UTC

Post by The Older Gentleman
But, agreed, I've never seen a four-cylinder bike with a single carb,
except possibly a Nimbus or Henderson.

Or the occasional ATP equipped UJM.

The Older Gentleman

2006-06-13 06:15:12 UTC

Post by James Clark

Post by The Older Gentleman
But, agreed, I've never seen a four-cylinder bike with a single carb,
except possibly a Nimbus or Henderson.

Or the occasional ATP equipped UJM.

Oh yes indeed :-))

--
Trophy 1200 750SS CB400F CD250 Morini 500 Sport
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

2006-06-12 15:17:14 UTC

Post by R. Pierce Butler
It is rather difficult to fit a single carb with an intake manifold on a
bike.

I saw a neautiful old 1970's era Triumph Trident fitted with a manifold
and a single carburetor.

The installation was sanitary, but horsepower output was severely
limited by the single
~30mm Amal carburetor. The owner wanted good low RPM throttle response
because the Trident was powering a sidecar rig.

Like Sammm said, it's necessary to keep the intake port velocity within
certain limits.

When you stick any kind of a manifold onto a small displacement engine
whose cylinders don't fire all that often at lower RPM, you can never
get the intake velocity up high enough to suck enough gasoline out of
the float bowl and the fuel droplets mix poorly.

The log type manifold just has far too much volume in the plenum, and
the engineer would have to employ the flask resonance formula to see
what frequency the manifold would resonate at.

I won't repeat the flask resonance formula, as I have posted it before.
But, even if you installed two carburetors on two, 2-legged manifolds
like my old Triumph TR-4 had, you would run into a problem with excess
volume of air in the manifold leg that went to the cylinder that wasn't
on the intake stroke.

A smart designer could probably make use of that air to give him a
boost at some RPM, but the kind of guy who is wondering why motorcycles
don't have a log manifold with one Stromberg 97 is unlikely to be a
"smart designer"...

There are *enough* problems inherent with getting good throttle
response out of a small displacement motorcycle engine that uses one
carburetor per cylinder, feeding through one intake port.

Gas velocity through a port = piston speed X (port area / cylinder bore
area )

Modern high performance engines need port velocities around 350 to 450
feet per second to have good throttle response.

Old British engines like the AJS-7R would hardly run with port
velocities down around
220 feet per second, and the almost-competitive Harley V-twin road
racers that were discontinued had such large intake ports they lacked
throttle response with intake port velocities around 300 feet per
second.

The Harley was fuel injected, so getting fuel into the system was no
problem. But the designer of the inlet ports was a NASCAR engine
builder (Roush), and he was designing the ports as if the Harley was
going to run wide open on super speedways.

The upper limit for intake port velocity is around 1100 feet per
second. Anything faster than that causes sonic shock waves that reduce
air flow.

2006-06-11 17:43:19 UTC

Getting frustrated by the complexity and mysteries of multiple carbs,
are you?

It's a lot easier to get to understand motorcycle carbs than it is to
re-engineer a single carburetor on a manifold and have it *work* on a
motorcycle engine.

Motorcycle inline 4's are like automotive inline 4's and inline 6's in
that the cylinders are all in a row.

Older automobile designs used simple "log" manifolds that were just a
simple large tube that bolted to the side of a 4 or 6-cylinder engine
and the carburetor bolted to the large tube. The middle two cylinders
would get a richer mixture if a simple log manifold was used. The end
cylinders would get a leaner mixture because the fuel/air mix had
further to travel.

Harley Davidsons use one carburetor for two cylinders, but it doesn't
work all that well.
At some speeds one cylinder hogs the gas from the other cylinder
because of the firing order. As I recall, there are only about 70
crankshaft degrees between the intake strokes of the two cylinders, so
one cylinder gets starved with only one carburetor.

More modern intake manifold designs paired the intake runners for
cylinders.

It's easy to see what is being done when there are two carbs on two
individual intake manifolds on the side of an inline 4 car engine.

My Triumph TR-4 had two long tuned manifolds with 1 carb on each
manifold. Each manifold fed two cylinders. The # 1 and # 2 cylinders
were fed by one manifold, the
# 3 and # 4 cylinders were fed by the other manifold.

Each intake track was about a foot long from the valve head to the
carburetor mouth.

The cylinders paired by the two intake mainfolds were 90 degrees apart
in their firing stroke. If you study the motions of the pistons and the
positions of the intake and exhaust valves, you will see that only one
intake valve is open at a time and that air is only being sucked
through one leg of one of the two manifolds.

If that's the case, why have two manifolds with two legs? It makes more
sense to use two carburetors on two intake tracks.

There just isn't much room behind a lower RPM motorcycle engine, if you
are going to use paired mainfolds like cars use.

Americans were inspired by the screaming high RPM European grand prix
racing during the 1960's, so racer styling was important to American
buyers.

Really high RPM engines don't need the long intake manifolds like my
TR-4 used. They can use really short intake tracts. The actual length
of the intake passage would be from the head of the closed intake valve
to the mouth of the carburetor. So it could be six or seven inches
long.

Italian motorcycle engineers began building inline-4's back in the
1950's that had
one carburetor and one exhaust pipe per cylinder. MV Agusta inspired
Honda to
follow the scheme. MV lent Honda their technical expertise.

The early one carb per cylinder Hondas didn't really produce a lot of
power in spite of their use of really high RPM. Some smaller Honda
grand prix engines turned an incredible 20,000 RPM. But the horsepower
output was just as incredibly low, compared to modern engines.

The individual grand prix racer cylinders did not "breathe" all that
well
because they didn't take advantage of intake and exhaust pulses from
the cylinders that were firing 180 degrees later.

George Kerker and a few other California hotrodders figured that if a
pair of tuned headers worked well on American V-8's, a single 4 into 1
header would do the same for an inline 4 motorcycle engine.

The problem was that the engines had a frustrating flat spot between
5000 and 7000 or 8000 RPM, and then they made great horsepower from
8000 RPM to whatever RPM the engine could stand. Up until just
recently, that was about 13,000 RPM, but
there is a 600 cc Yamaha engine that turns 18,000 RPM now.

It has 4 individual fuel injector bodies.

Motorcycle engineers have taken another trick from the automotive
performance book.

They use tuned air boxes called "Helmholtz Resonators" to feed the
individual carburetor. The air boxes overcome adverse pressure waves
that try to drive air backwards out of the carburetors or throttle
bodies.

m***@merr.com

2006-06-11 20:54:52 UTC

Your in depth explanation is very much appreciated.
Thanks