Discussion:
2 stroke bogs/dies when approacing idle.
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Josh Assing
2005-08-30 19:56:58 UTC
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I have a KTM 250 that runs great, as long as you keep the revs up.
if you let it approach idle, it starts to bog; then dies. once it starts to
bog; it's almost impossible to "revive" but it restarts w/o problem.

The plug looks normal; so I"m going with it's not getting too much fuel.

The carb boot looks cracked; but can't find any "for sure" cracks that go all
the way thru.

Could the bike be sucking too much air and causing this 'bogging/death' I'm
experiencing?

Thanks
-josh


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krusty kritter
2005-08-30 21:23:47 UTC
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Post by Josh Assing
I have a KTM 250 that runs great, as long as you keep the revs up.
if you let it approach idle, it starts to bog; then dies. once it starts to
bog; it's almost impossible to "revive" but it restarts w/o problem.
The plug looks normal; so I"m going with it's not getting too much fuel.
If you think it's the carb, clean out the idle jet with aerosol
carburetor cleaner. You can probably clean out the idle passages by
squirting aerosol cleaner down the pilot air jet which should be in the
air intake bell of the carb. Then, screw the pilot air screw all the
way in, until it lightly bottoms out, counting the turns and fractions
of turns. Write that number down. Then, unscrew the pilot air screw and
remove it. Make sure you get the little spring, washer and o-ring if
there is a washer and o-ring in the hole. Then, squirt aerosol carb
cleaner down the hole the pilot air screw came out of. Carb cleaner
should come back out the pilot air jet, out the idle jet into the float
bowl and out the idle bypass discharge port downstream of the throttle
slide.

I don't recommend squirting a lot of aerosol carb cleaner into the
pilot air screw hole if it's going to run down into the intake port.

Then, reassemble the spring, washer and little o-ring on the pilot air
screw and screw it back in until it lightly bottoms. Then turn the
pilot air screw back out the same number of turns you wrote down and
ride the bike. If it still
bogs and dies, try turning the idle speed UP just a little and turn the
pilot air screw CLOCKWISE 1/4 of a turn and see what happens.
Post by Josh Assing
The carb boot looks cracked; but can't find any "for sure" cracks that go all
the way thru.
Well, does the engine sound "asthmatic"? Does it *wheeze* just before
it quits?

Buy a tube a black RTV silicone rubber sealer and coat the entire carb
boot and let the RTV cure for 8 hours and then ride the bike and see
what happens.
Post by Josh Assing
Could the bike be sucking too much air and causing this 'bogging/death' I'm
experiencing?
You could try squirting water or WD40 at the cracks while the engine is
running.
If the idle speed changes temporarily, you can bet that the rubber boot
leaks air...
Josh Assing
2005-08-30 23:13:50 UTC
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Post by krusty kritter
If you think it's the carb, clean out the idle jet with aerosol
Actually, I don't think it is anymore; turning up the idle screw didn't help --
you had to keep blipping the throttle..
Post by krusty kritter
Well, does the engine sound "asthmatic"? Does it *wheeze* just before
it quits?
No.. Good point. It just REV-REV-REV-REV-(let down too much)
RRrrrrrrr<pthttt>(done) if you WOT when it starts to bog down; it doesn't help.
Post by krusty kritter
You could try squirting water or WD40 at the cracks while the engine is
running.
If the idle speed changes temporarily, you can bet that the rubber boot
leaks air...
Any other ideas on it?


Thanks!
-josh


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krusty kritter
2005-08-31 01:57:49 UTC
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Post by Josh Assing
Any other ideas on it?
Got reed valves? Maybe it's a reed petal that doesn't quite close and
the
piston blows back through the carb so it doesn't have enough vacuum to
suck
fuel/air mix in at low engine RPM...

Other possible problems for stalling are:

Fouled spark plug
Dirty ignition points (if you have points)
Wrong ignition timing
Clogged fuel line
Clogged jets
Crankcase compression leak
Intake manifold leak
Old gasoline has lost it's "ooomph!"
Josh Assing
2005-08-31 03:07:26 UTC
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Post by krusty kritter
Fouled spark plug
nope
Post by krusty kritter
Dirty ignition points (if you have points)
none
Post by krusty kritter
Wrong ignition timing
Doubtful.. but possible.
Post by krusty kritter
Clogged fuel line
Clogged jets
no & no
Post by krusty kritter
Crankcase compression leak
GOOD ONE! I forgot about crank cases...
Post by krusty kritter
Intake manifold leak
well; that is what I'm thinking....
Post by krusty kritter
Old gasoline has lost it's "ooomph!"
it is old and varnishy...maybe a change...

Thanks
-josh


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Nemo
2005-08-31 16:51:05 UTC
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Post by Josh Assing
Post by krusty kritter
Fouled spark plug
nope
Post by krusty kritter
Dirty ignition points (if you have points)
none
Post by krusty kritter
Wrong ignition timing
Doubtful.. but possible.
Post by krusty kritter
Clogged fuel line
Clogged jets
no & no
Post by krusty kritter
Crankcase compression leak
GOOD ONE! I forgot about crank cases...
Post by krusty kritter
Intake manifold leak
well; that is what I'm thinking....
Post by krusty kritter
Old gasoline has lost it's "ooomph!"
it is old and varnishy...maybe a change...
Thanks
-josh
Two-strokes are super sensitive to stale gasoline.

Ed Cregger

Nemo
2005-08-30 22:57:12 UTC
Permalink
Post by Josh Assing
I have a KTM 250 that runs great, as long as you keep the revs up.
if you let it approach idle, it starts to bog; then dies. once it starts to
bog; it's almost impossible to "revive" but it restarts w/o problem.
The plug looks normal; so I"m going with it's not getting too much fuel.
The carb boot looks cracked; but can't find any "for sure" cracks that go all
the way thru.
Could the bike be sucking too much air and causing this 'bogging/death' I'm
experiencing?
Thanks
-josh
---
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Yes, what you are describing is common to a two-stroke that is running too
lean on the low end. Your suspicion about an air leak is what I would
pursue, unless you have reason to believe that the low speed settings have
been diddled with lately.

Ed Cregger
Josh Assing
2005-08-31 03:07:25 UTC
Permalink
Thanks Ed.

I can't find the carb boot for this darn bike anywhere... slathering rtv is
only a stop cap measure in my book...
Post by Nemo
Post by Josh Assing
I have a KTM 250 that runs great, as long as you keep the revs up.
if you let it approach idle, it starts to bog; then dies. once it starts to
bog; it's almost impossible to "revive" but it restarts w/o problem.
The plug looks normal; so I"m going with it's not getting too much fuel.
The carb boot looks cracked; but can't find any "for sure" cracks that go all
the way thru.
Could the bike be sucking too much air and causing this 'bogging/death' I'm
experiencing?
Thanks
-josh
---
Remove x's to send.
Yes, what you are describing is common to a two-stroke that is running too
lean on the low end. Your suspicion about an air leak is what I would
pursue, unless you have reason to believe that the low speed settings have
been diddled with lately.
Ed Cregger
---
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