How do you clean a Mikuni BS28 CV carburetor USA model?

[mike]

How do you clean a Mikuni BS28 CV carburetor USA model?

I bought a 2007 Kawasaki Eliminator 125 (BN125-A8) with 423 miles on it
that had been sitting garaged for 5 years.
I drained the carb and tank. I was amazed at how clean the effluent
was.
But it's running very lean and changing characteristics.
Needs to be cleaned.

This carb is 30 years newer than my previous experience
and has pollution control stuff on it.

Normally, I'd just disassemble it, shoot it full of B12 Chemtool
and stick it in the ultrasonic cleaner.

This carb has a plastic main jet piston and rubber diaphragms
on the piston and the coasting enricher.
The manual also mentions that there are non-removable plastic parts
inside and warns about harsh chemicals with no actual guidance
on where those parts are or what chemicals are permissible/safe.

B12 Chemtool contains all manner of chemicals including
Toluene and Acetone. I'm afraid to put that in this
carb.

I have to remove a bunch of stuff to get at the carb on this
bike. I don't want to do it more than once.
Yes, I did buy a fuel filter.

So, what chemicals and methods does one use to clean
this carb without destroying it?

Is there anything safe and effective to add to gas?
SeaFoam gets a lot of hype Mostly Naptha.
Just pouring something into the gas is a lot more
attractive than disassembly, if I could be confident
that it wouldn't hurt anything.

[Kevin Bottorff]

Post by mike
How do you clean a Mikuni BS28 CV carburetor USA model?
I bought a 2007 Kawasaki Eliminator 125 (BN125-A8) with 423 miles on it
that had been sitting garaged for 5 years.
I drained the carb and tank. I was amazed at how clean the effluent
was.
But it's running very lean and changing characteristics.
Needs to be cleaned.
This carb is 30 years newer than my previous experience
and has pollution control stuff on it.
Normally, I'd just disassemble it, shoot it full of B12 Chemtool
and stick it in the ultrasonic cleaner.
This carb has a plastic main jet piston and rubber diaphragms
on the piston and the coasting enricher.
The manual also mentions that there are non-removable plastic parts
inside and warns about harsh chemicals with no actual guidance
on where those parts are or what chemicals are permissible/safe.
B12 Chemtool contains all manner of chemicals including
Toluene and Acetone. I'm afraid to put that in this
carb.
I have to remove a bunch of stuff to get at the carb on this
bike. I don't want to do it more than once.
Yes, I did buy a fuel filter.
So, what chemicals and methods does one use to clean
this carb without destroying it?
Is there anything safe and effective to add to gas?
SeaFoam gets a lot of hype Mostly Naptha.
Just pouring something into the gas is a lot more
attractive than disassembly, if I could be confident
that it wouldn't hurt anything.

sea foam won`t hurt anything in your carbs. I would put a doubble
strength dose of it in a tank and run it out first. Have had good luck
getting that to free up the carbs. if that doesn`t work then you can try
something more aggressive. Its very possible that those vv carbs will
loosen up and run better with some use. KB

[mike]

Post by Kevin Bottorff

Post by mike
How do you clean a Mikuni BS28 CV carburetor USA model?
I bought a 2007 Kawasaki Eliminator 125 (BN125-A8) with 423 miles on it
that had been sitting garaged for 5 years.
I drained the carb and tank. I was amazed at how clean the effluent
was.
But it's running very lean and changing characteristics.
Needs to be cleaned.
This carb is 30 years newer than my previous experience
and has pollution control stuff on it.
Normally, I'd just disassemble it, shoot it full of B12 Chemtool
and stick it in the ultrasonic cleaner.
This carb has a plastic main jet piston and rubber diaphragms
on the piston and the coasting enricher.
The manual also mentions that there are non-removable plastic parts
inside and warns about harsh chemicals with no actual guidance
on where those parts are or what chemicals are permissible/safe.
B12 Chemtool contains all manner of chemicals including
Toluene and Acetone. I'm afraid to put that in this
carb.
I have to remove a bunch of stuff to get at the carb on this
bike. I don't want to do it more than once.
Yes, I did buy a fuel filter.
So, what chemicals and methods does one use to clean
this carb without destroying it?
Is there anything safe and effective to add to gas?
SeaFoam gets a lot of hype Mostly Naptha.
Just pouring something into the gas is a lot more
attractive than disassembly, if I could be confident
that it wouldn't hurt anything.

sea foam won`t hurt anything in your carbs. I would put a doubble

Interesting misspelling. I have the same problem with trippple. ;-)
I know better, but I always type three p's.

Post by Kevin Bottorff
strength dose of it in a tank and run it out first. Have had good luck
getting that to free up the carbs. if that doesn`t work then you can try
something more aggressive. Its very possible that those vv carbs will
loosen up and run better with some use. KB

Thanks, but the whole point of my post was to determine exactly what is
more aggressive and won't damage the carb.
Exactly what chemicals can I use?

[bob prohaska]

Post by mike
Thanks, but the whole point of my post was to determine exactly what is
more aggressive and won't damage the carb.
Exactly what chemicals can I use?

As always, YMMV, but I've had reasonable luck on SV650S carbs using
hot Pine-Sol. It's glycolic acid solution in water, so it won't do
much to plastic and rubber. It will etch zinc, so galvanized steel
and brass both get stripped and the brass turns pink. It doesn't seem
to etch carb body material too badly, but I'd watch closely during
the soak. I used the Pine-Sol on a hot plate, not quite simmering.
IIRC it took around an hour. Rinse with clean water, dry and assemble.

Before doing anything else, I'd put good quality gas in the bike
and ride it some. It might clean up on its own. Emission controlled
carbs are lean, a small tweak of the idle mixture could do what you
want.

If you do take the carb apart, check for welch plugs over the idle and
low speed fuel ports to the carb throat. If they're present, and the
carb won't improve with immersion in cleaner, it might pay to remove
them, clean the chambers underneath and install new plugs. Hopefully
less drastic measures will suffice.

hth,

bob prohaska

[mike]

Post by bob prohaska

Post by mike
Thanks, but the whole point of my post was to determine exactly what is
more aggressive and won't damage the carb.
Exactly what chemicals can I use?

As always, YMMV, but I've had reasonable luck on SV650S carbs using
hot Pine-Sol. It's glycolic acid solution in water, so it won't do
much to plastic and rubber. It will etch zinc, so galvanized steel
and brass both get stripped and the brass turns pink. It doesn't seem
to etch carb body material too badly, but I'd watch closely during
the soak. I used the Pine-Sol on a hot plate, not quite simmering.
IIRC it took around an hour. Rinse with clean water, dry and assemble.
Before doing anything else, I'd put good quality gas in the bike
and ride it some. It might clean up on its own. Emission controlled
carbs are lean, a small tweak of the idle mixture could do what you
want.
If you do take the carb apart, check for welch plugs over the idle and
low speed fuel ports to the carb throat. If they're present, and the
carb won't improve with immersion in cleaner, it might pay to remove
them, clean the chambers underneath and install new plugs. Hopefully
less drastic measures will suffice.

Seems to be only one plug over the pilot adjustment.
The actual jet seems to be accessible inside the bowl.
I put a colder plug in it,
Poured some seafoam in the gas,
Backed the pilot adjustment way out.
Been running it intermittently to keep the seafoam distributed.
Seems to be helping a lot.
Put the pilot adjustment back where it was and it's mostly running.
I'm optimistic.
Thanks, mike

Post by bob prohaska
hth,
bob prohaska

[bob prohaska]

Post by mike
Seems to be only one plug over the pilot adjustment.

That's probably the anti-tamper plug. It'll have to go.
The welch plug I'm talking about (which you may not have)
was over the series of hair-fine drillings in the carb
throat where the rising edge of the throttle butterfly
passes.

Post by mike
The actual jet seems to be accessible inside the bowl.
I put a colder plug in it,

That's a surprise, what motivated a colder plug?

Post by mike
Poured some seafoam in the gas,
Backed the pilot adjustment way out.

Did you take it out and look? There was junk on the end of
one pilot needle on my SV.

Post by mike
Been running it intermittently to keep the seafoam distributed.
Seems to be helping a lot.
Put the pilot adjustment back where it was and it's mostly running.
I'm optimistic.
Thanks, mike

You're welcome, good luck!

bob prohaska

[mike]

Post by bob prohaska

Post by mike
Seems to be only one plug over the pilot adjustment.

That's probably the anti-tamper plug. It'll have to go.
The welch plug I'm talking about (which you may not have)
was over the series of hair-fine drillings in the carb
throat where the rising edge of the throttle butterfly
passes.

Post by mike
The actual jet seems to be accessible inside the bowl.
I put a colder plug in it,

That's a surprise, what motivated a colder plug?

Somebody suggested it.
The plug insulator was whiter than white; couldn't hurt.
I figgered $4 was a cheap investment to try to reduce the
detonation while the carb cleaning got sorted out.
Just grabbing at straws to stave off disassembling the bike
to get the carb out.
The people who design bikes should be forced to work in the
service department using only the tools in a typical guy's
toolbox until their hands bleed before being allowed
to configure a bike. It's as if nobody in the design department
ever tried to fix a motorcycle. Grrrr!

Post by bob prohaska

Post by mike
Poured some seafoam in the gas,
Backed the pilot adjustment way out.

Did you take it out and look? There was junk on the end of
one pilot needle on my SV.

Everything I looked at was clean, clean, clean.
I'd drained the carb and fuel tank twice, nothing.
I put in a see-thru fuel filter, nothing.

Post by bob prohaska

Post by mike
Been running it intermittently to keep the seafoam distributed.
Seems to be helping a lot.
Put the pilot adjustment back where it was and it's mostly running.
I'm optimistic.
Thanks, mike

You're welcome, good luck!
bob prohaska

[mike]

Post by bob prohaska

Post by mike
Seems to be only one plug over the pilot adjustment.

That's probably the anti-tamper plug. It'll have to go.
The welch plug I'm talking about (which you may not have)
was over the series of hair-fine drillings in the carb
throat where the rising edge of the throttle butterfly
passes.

Post by mike
The actual jet seems to be accessible inside the bowl.
I put a colder plug in it,

That's a surprise, what motivated a colder plug?

Post by mike
Poured some seafoam in the gas,
Backed the pilot adjustment way out.

Did you take it out and look? There was junk on the end of
one pilot needle on my SV.

Post by mike
Been running it intermittently to keep the seafoam distributed.
Seems to be helping a lot.
Put the pilot adjustment back where it was and it's mostly running.
I'm optimistic.
Thanks, mike

You're welcome, good luck!
bob prohaska

The saga continues...
2007 Kawasaki Eliminator BN125A7
USA NOT California
Carb Mikuni BS28
Had 423 Miles, now 1050.

Was running very lean.
Hanging idle.
Exhaust pipe is turning dark.

Seafoam and some adjustment of the pilot screw
fixed the hanging idle.

Was detonating in almost every throttle range
on acceleration.

I've found very little on the web related to this bike.
What little there is is heavily weighted toward,
"It's running too rich," but not much in the way
of solutions.

Disassembled the carburetor.
Fuel level was below the lower spec limit, so I adjusted
the float to put the fuel level at the high limit.

I couldn't get the pilot jet out. Decided to leave
breaking that for another day. I did blow air thru it
and used a vacuum pump to suck cleaning solution
back thru it. (water and simple green)
I was afraid to try anything with acetone because of
manual warning about non-removable plastic parts inside.
I can get liquid to flow out all the tiny holes in the venturi.
Let it sit in the ultrasonic cleaner for 15 minutes while
I forced liquid thru every orifice and sucked it back with
the vacuum pump.

Now, much more responsive at high RPM.
Engine sounds good over 25 MPH in 5th gear.
I think that part is doing as well as I can expect for a 125.

Low RPM sounds like it might be a little rich.
Still detonating slightly around 4K RPM depending on
gear and load.
I cranked the pilot screw out to 3.5 turns
to reduce the detonation. Helps, but
doesn't change if I go further.
Runs OK at low RPM and low or high throttle.
Problem is that it pings at about 1/4 throttle
at low speed.

The tuning instructions that I've read for CV carbs
lead me to believe that the main jet is OK.
The main jet needle is not adjustable.
I think I may need a bigger pilot jet so I can
set the adjustment tighter for low end
and still get more gas in the 1/4 throttle area.

I don't understand exactly what I'm hearing.
My experience is with bikes at least 20 years older,
before the emissions stuff got added.

When the mixture is rich, you get a blubbery/farty
sound. When it's lean, you get a crack-crack sound
from detonation high speed explosion.

What I'm hearing is a blubbery sound at low
RPM and the crack-crack as the engine speed
increases, but the blubbery sound is still there.
The crack-crack disappears as the RPM continues
to increase.
How can it be rich and lean at the same RPM?
What am I misunderstanding?

I could use some advice on choosing a pilot jet.

Is there a trick to getting the pilot jet out?
I had a screwdriver with a good fit and twisted
on it so hard I was afraid I'd break something.

I also had a problem with the float hinge. It's pressed in.
Manual warns not to beak the hinge mounts. Can't tell
which side has the press fit and supporting the wrong
end can't end well. I banged on the pin as hard as I dared
without success. Float valve doesn't seem to have a problem,
so I left it alone. Wonder if heating or cooling it with freon
will loosen it up. Not sure what the parts are made of and
the relative expansion coefficients.

Anybody got any experience with the 6Sigma carburetor kits.
They claim to design a jet system specifically tailored to your
situation. I hate to drop $50 on a vague promise.
On the other hand, I'd drop $50 in a minute if I had confidence
that it would solve my detonation problem. I'm otherwise happy
with the performance of the bike. A 5% performance increase
and still detonating is not worth $50 to me.

I talked with two local Kawasaki service departments. Nobody would
admit to ever having worked on an eliminator 125. I'm skeptical
that the 6Sigma people have tried every bike that they claim to support.

I'm operating on the assumption that any detonation is a serious issue.
Am I worrying too much?

Advice?
Thanks, mike

[bob prohaska]

Post by mike
I'm operating on the assumption that any detonation is a serious issue.
Am I worrying too much?

Not until you know why.

Post by mike
Advice?

Check the timing and TPS if it has one.

Post by mike
Thanks, mike

HTH,

bob prohaska

[mike]

Post by bob prohaska

Post by mike
I'm operating on the assumption that any detonation is a serious issue.
Am I worrying too much?

Not until you know why.

Post by mike
Advice?

Check the timing and TPS if it has one.

Post by mike
Thanks, mike

HTH,
bob prohaska

What's a TPS?

The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then advanced
a LOT over some narrow midrange, then stayed at that level for the
remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

Say that I took the cover off and measured the advance.
How do I know whether that is good or bad? What would I do about
it if I decided it was wrong?

The thing doesn't have a tach, so I'd have to build one.
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to be
heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

[bob prohaska]

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance" unit
found on autos with Kettering (points and condenser) ignition.

Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong information
to the ignition control which is apt to give wrong spark timing.

A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then advanced
a LOT over some narrow midrange, then stayed at that level for the
remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to be
heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

HTH,

bob prohaska

[mike]

Post by bob prohaska

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance" unit
found on autos with Kettering (points and condenser) ignition.
Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong information
to the ignition control which is apt to give wrong spark timing.
A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then advanced
a LOT over some narrow midrange, then stayed at that level for the
remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Have the manual. Timing marks were easily identifiable
when I checked the valve settings.

Post by bob prohaska

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

I was gonna use the scope as a tach. It has a frequency readout
if you can see 3 or more pulses. I was gonna use a clamp on
current probe around the plug wire.

I do have several timing strobes. One has a tach, but it's designed
for 6-8 cylinders. With only one cylinder, you end up multiplying
a very small number at idle. Then there's the issue of the waste
spark.

Post by bob prohaska

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to be
heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

Ok, but if I can't change the timing, all I can tell if it's working
or not working. The angle doesn't seem to be variable at all.
Compensation does not seem to be an option.

Post by bob prohaska
HTH,
bob prohaska

I tried a different experiment. I covered about 40% of the air filter
element with plastic sheet.
I didn't even get out of the driveway.
Changed it to about 15%. Still HORRIBLY rich...not drivable.
I expected it to get richer, but this degree surprised me.
You could get 15% variation from the kind of oil you put
on the filter element.

I've had several bikes over the years from 50cc to 550cc.
I don't remember any of them being anywhere near this temperamental.

[Kevin Bottorff]

Post by mike

Post by bob prohaska

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance"
unit found on autos with Kettering (points and condenser) ignition.
Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong
information to the ignition control which is apt to give wrong spark
timing.
A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then
advanced a LOT over some narrow midrange, then stayed at that level
for the remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively
speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Have the manual. Timing marks were easily identifiable
when I checked the valve settings.

Post by bob prohaska

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

I was gonna use the scope as a tach. It has a frequency readout
if you can see 3 or more pulses. I was gonna use a clamp on
current probe around the plug wire.
I do have several timing strobes. One has a tach, but it's designed
for 6-8 cylinders. With only one cylinder, you end up multiplying
a very small number at idle. Then there's the issue of the waste
spark.

Post by bob prohaska

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to
be heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

Ok, but if I can't change the timing, all I can tell if it's working
or not working. The angle doesn't seem to be variable at all.
Compensation does not seem to be an option.

Post by bob prohaska
HTH,
bob prohaska

I tried a different experiment. I covered about 40% of the air filter
element with plastic sheet.
I didn't even get out of the driveway.
Changed it to about 15%. Still HORRIBLY rich...not drivable.
I expected it to get richer, but this degree surprised me.
You could get 15% variation from the kind of oil you put
on the filter element.
I've had several bikes over the years from 50cc to 550cc.
I don't remember any of them being anywhere near this temperamental.

thats because its messing with the vv carbs to much vacume where it
shouldnt be. its easy to increase the main jet needle. I just used a
small metric flat washer under it to raise it up for a richer cruse rpm.
wont affect the wide open throttle or idle. KB
PS if you need more than one washer you will need to sand the bottom of
the needle retainer plug so there is still a slight movement of the
needle when tight.

[mike]

Post by Kevin Bottorff

Post by mike

Post by bob prohaska

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance"
unit found on autos with Kettering (points and condenser) ignition.
Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong
information to the ignition control which is apt to give wrong spark
timing.
A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then
advanced a LOT over some narrow midrange, then stayed at that level
for the remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively
speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Have the manual. Timing marks were easily identifiable
when I checked the valve settings.

Post by bob prohaska

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

I was gonna use the scope as a tach. It has a frequency readout
if you can see 3 or more pulses. I was gonna use a clamp on
current probe around the plug wire.
I do have several timing strobes. One has a tach, but it's designed
for 6-8 cylinders. With only one cylinder, you end up multiplying
a very small number at idle. Then there's the issue of the waste
spark.

Post by bob prohaska

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to
be heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

Ok, but if I can't change the timing, all I can tell if it's working
or not working. The angle doesn't seem to be variable at all.
Compensation does not seem to be an option.

Post by bob prohaska
HTH,
bob prohaska

I tried a different experiment. I covered about 40% of the air filter
element with plastic sheet.
I didn't even get out of the driveway.
Changed it to about 15%. Still HORRIBLY rich...not drivable.
I expected it to get richer, but this degree surprised me.
You could get 15% variation from the kind of oil you put
on the filter element.
I've had several bikes over the years from 50cc to 550cc.
I don't remember any of them being anywhere near this temperamental.

thats because its messing with the vv carbs to much vacume where it
shouldnt be. its easy to increase the main jet needle. I just used a
small metric flat washer under it to raise it up for a richer cruse rpm.
wont affect the wide open throttle or idle. KB
PS if you need more than one washer you will need to sand the bottom of
the needle retainer plug so there is still a slight movement of the
needle when tight.

Thanks, I'll try that next time I have it open.
I'm still wondering if that is the problem.
High RPM cruising isn't the problem.
This bike is so low power and low geared that anything over
30 MPH is high RPM.
My problem is down at 1/4-1/2 throttle accelerating.
Cruising at any RPM sounds just fine.

The service manual is a little confusing.
It says the pilot screw is supposed to be out 1-5/8 turns.
That's about where mine was stock.
There's also another unannotated line that says 3.0 (BN125A7)
which is the one I have.

If I increase the pilot jet, shouldn't that richen it up where
the problem area lies, also increase top end slightly and allow
me to tighten the pilot screw to lean the lowest speeds a little?
Sounds like that should address all the issues. What am I missing?

[mike]

Post by Kevin Bottorff

Post by mike

Post by bob prohaska

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance"
unit found on autos with Kettering (points and condenser) ignition.
Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong
information to the ignition control which is apt to give wrong spark
timing.
A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then
advanced a LOT over some narrow midrange, then stayed at that level
for the remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively
speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Have the manual. Timing marks were easily identifiable
when I checked the valve settings.

Post by bob prohaska

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

I was gonna use the scope as a tach. It has a frequency readout
if you can see 3 or more pulses. I was gonna use a clamp on
current probe around the plug wire.
I do have several timing strobes. One has a tach, but it's designed
for 6-8 cylinders. With only one cylinder, you end up multiplying
a very small number at idle. Then there's the issue of the waste
spark.

Post by bob prohaska

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to
be heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

Ok, but if I can't change the timing, all I can tell if it's working
or not working. The angle doesn't seem to be variable at all.
Compensation does not seem to be an option.

Post by bob prohaska
HTH,
bob prohaska

I tried a different experiment. I covered about 40% of the air filter
element with plastic sheet.
I didn't even get out of the driveway.
Changed it to about 15%. Still HORRIBLY rich...not drivable.
I expected it to get richer, but this degree surprised me.
You could get 15% variation from the kind of oil you put
on the filter element.
I've had several bikes over the years from 50cc to 550cc.
I don't remember any of them being anywhere near this temperamental.

thats because its messing with the vv carbs to much vacume where it
shouldnt be. its easy to increase the main jet needle. I just used a
small metric flat washer under it to raise it up for a richer cruse rpm.
wont affect the wide open throttle or idle. KB
PS if you need more than one washer you will need to sand the bottom of
the needle retainer plug so there is still a slight movement of the
needle when tight.

Can you recommend a thickness for this washer?
I'll give it a try.
Thanks, mike

[Kevin Bottorff]

Post by mike

Post by Kevin Bottorff

Post by mike

Post by bob prohaska

Post by mike
What's a TPS?

Throttle position sensor. It's a surrogate for the "vacuum advance"
unit found on autos with Kettering (points and condenser) ignition.
Crudely put, timing needs to advance with speed and retard with
manifold absolute pressure. Absolute pressure measurements are sort
of a pain, but some bright fellow figured out that if you know the
throttle angle and engine speed manifold pressure can be worked out
for any given engine. It's usually a variable resistor mounted on the
throttle butterfly shaft. If it's not working, it sends wrong
information to the ignition control which is apt to give wrong spark
timing.
A TPS can be checked with an ohmmeter out of circuit, or a voltage
measurement in-circuit if you can get at the terminals. You'll need
a manual to indicate the correct values, I don't think they're standardized.

Post by mike
The article I read was general, not related to this particular bike.
It suggested that timing was fixed for the low RPM range, then
advanced a LOT over some narrow midrange, then stayed at that level
for the remainder of the speed range.
I could infer that the advance is starting too early.
I'm not convinced that fits with the symptoms.

It may not be the problem, but it's an easy test, relatively speaking.

Post by mike
Say that I took the cover off and measured the advance.
How do I know whether that is good or bad?

You need the manual to identify the timing marks.

Have the manual. Timing marks were easily identifiable
when I checked the valve settings.

Post by bob prohaska

Post by mike
What would I do about
it if I decided it was wrong?

Start replacing parts, unless you can find a bad connection.

Post by mike
The thing doesn't have a tach, so I'd have to build one.

If it's wrong enough, you might not need a tach. Finding advanced
timing at dead slow idle would be a strong hint.

Post by mike
I have a Snap-On automotive scope, but the spark pulse width is
too short. By the time I set the sweep speed low enough to see
two sparks, the sampling interval is too coarse to catch them all.

I don't think an oscilloscope will tell you timing, generally.
A timing strobe is more likely to help.

I was gonna use the scope as a tach. It has a frequency readout
if you can see 3 or more pulses. I was gonna use a clamp on
current probe around the plug wire.
I do have several timing strobes. One has a tach, but it's designed
for 6-8 cylinders. With only one cylinder, you end up multiplying
a very small number at idle. Then there's the issue of the waste
spark.

Post by bob prohaska

Post by mike
I realize that it's not conclusive, but many of the posts regarding
this bike are about it running too lean. Making it richer seems to
be heading in the right direction, I just need more of it.
Which keeps leading me back to the pilot jet as the most leverage.

Carb problems are common, ignition problems seem to be much rarer
and usually of the "no spark" variety. Your case might be one of
the exceptions. Both mixture and timing affect detonation tendencies
and one can compensate for the other to some degree.

Ok, but if I can't change the timing, all I can tell if it's working
or not working. The angle doesn't seem to be variable at all.
Compensation does not seem to be an option.

Post by bob prohaska
HTH,
bob prohaska

I tried a different experiment. I covered about 40% of the air filter
element with plastic sheet.
I didn't even get out of the driveway.
Changed it to about 15%. Still HORRIBLY rich...not drivable.
I expected it to get richer, but this degree surprised me.
You could get 15% variation from the kind of oil you put
on the filter element.
I've had several bikes over the years from 50cc to 550cc.
I don't remember any of them being anywhere near this temperamental.

thats because its messing with the vv carbs to much vacume where it
shouldnt be. its easy to increase the main jet needle. I just used a
small metric flat washer under it to raise it up for a richer cruse rpm.
wont affect the wide open throttle or idle. KB
PS if you need more than one washer you will need to sand the bottom of
the needle retainer plug so there is still a slight movement of the
needle when tight.

Can you recommend a thickness for this washer?
I'll give it a try.
Thanks, mike

its been so long I dont remember the thickness. when I did it I used a
old adj needle to see appx. what I needed and found a small washer close
and trimed it to fit. I use a metric washer as they tend to be thinner.
anything will be better on those old lean running carbs. I never messed
with the pilot jet as your off that sooner than you think. KB

[The Older Gentleman]

Post by mike
So, what chemicals and methods does one use to clean
this carb without destroying it?

Get an ultrasonic cleaner. You'll use it for a lot more than just
cleaning carbs, and they're surprisingly cheap. Amazing things.

[mike]

Post by The Older Gentleman

Post by mike
So, what chemicals and methods does one use to clean
this carb without destroying it?

Get an ultrasonic cleaner. You'll use it for a lot more than just
cleaning carbs, and they're surprisingly cheap. Amazing things.

As I stated in my original post, an ultrasonic cleaner is my usual
device. What chemicals would one use as the media that won't hurt
the plastic/rubber stuff in the carb?

I'd also like to hear some comments on how ultrasonic cleaners
work in carb cleaning.

IIRC, cavitation is the process. Does a great job getting the outside
clean.
But what about all those twisty passages inside of a massive object.
By the time the shock wave gets thru the tiny holes, down the narrow
passages and into the place that's gummed up, is there any energy left?

[bob prohaska]

Post by mike
But what about all those twisty passages inside of a massive object.
By the time the shock wave gets thru the tiny holes, down the narrow
passages and into the place that's gummed up, is there any energy left?

Comparatively little, but it's better than nothing.

8-)

It's worth pointing out that ultrasonic cleaners get hot, as a
side effect. That certainly helps. But, chemistry is the key.

bob prohaska

[The Older Gentleman]

Post by mike
As I stated in my original post,

Ah yes, so you did.

[k***@uci.edu]

Hi I have the same motorcycle for 2002. I opened the carb and cleaned it. Now when I turn on the engine and give some gas, the rpm suddenly go up and when I adjust the idle screw to set it down the bike turns off. Could anyone tell me the origin of this issue? Also, I looked for this mikuni BS 28 carburetor all over the internet and did not find anything. Is there any website that sell this type of carburetor so I can replace it ?

[The Older Gentleman]

<***@uci.edu> wrote:

<snip>

How old is the post to which you are replying?

[Corvid]

Post by The Older Gentleman
<snip>
How old is the post to which you are replying?

http://al.howardknight.net/?STYPE=msgid&MSGI=%3Cokfar6%24h54%241%40dont-email.me%3E

It's lowercase mike.