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Thread: Carb problem

  1. #1
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    Carb problem

    This winter I rebuilt my carbs on my 92 RT. Cleaned carbs. Made sure the jets were clear. Installed new O rings,5 of them in each carb. New floats the ones that ride up on posts, of course it has new bowls. New diaphrams and gaskets. Marked the throttle and choke cable adjusters and returned them to the previous positions. Just started the bike, of course it started out with empty bowls. Flicked on choke, hit the starter and the thing fired right up.Took bike around block and it ran ok. Got back to house pulled in the clutch, let off the gas and it stalled. Started it back up revved it a couple of times , returned throttle to idle and it stalled. Just will not idle. If I gas it it runs good. Thought it maybe was flooding, pulled bowls and bent the tabs that the floats push on to control the amount of gas, still no idle. Pulled carbs and went back over instructions and checked things out and still no idle. I then restarted bike with the bowls being empty again. idled great with choke on , it started to die I gave it some throttle and turned off the choke and it purred along, again backed off the gas and it stalled again, no idle. Checked to make sure the little screws that you put into one of the holes in the corner of the bowls were there and they are. Instructions said without them the bike wouldn't idle. What should I do next??? Should I play with the throttle cable adjusters on the carbs???
    I have met the enemy, and he is us
    2011 R 1200 RT
    1992R100RT
    2007 Roadstar Midnight Silverado

  2. #2
    Registered User mneblett's Avatar
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    Sounds like the base idle simply isn't set high enough (i'm assuming of course, that you are riding the bike long enough to let it fully warm up -- a minute or so isn't enough to expect an airhead engine to run without at least some choke).

    Have you adjusted the idle stop screws to get the base idle up to ~1000-1100 rpm?

    If the idle screws are not holding the butterflies open a hair, no air can pass through the carb. They need to be screwed in enough to touch the throttle plate arm, plus an amount further in to crack the throttle plate open enough to let the required amount of idle air pass through.

  3. #3
    fracture
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    Quote Originally Posted by mneblett View Post
    Sounds like the base idle simply isn't set high enough (i'm assuming of course, that you are riding the bike long enough to let it fully warm up -- a minute or so isn't enough to expect an airhead engine to run without at least some choke).

    Have you adjusted the idle stop screws to get the base idle up to ~1000-1100 rpm?

    If the idle screws are not holding the butterflies open a hair, no air can pass through the carb. They need to be screwed in enough to touch the throttle plate arm, plus an amount further in to crack the throttle plate open enough to let the required amount of idle air pass through.
    Agreed. It has to be fully warmed up and the idle speed screw has to make contact with the throttle stop plate.

    Did you change this screw setting when you did the carb work?

  4. #4
    Registered User 88bmwjeff's Avatar
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    Apart from the idle setting as indicated above, are you sure you have the idle mixture set properly? Those initial settings are just starting points, and need to be adjusted once the engine is warmed up.
    Jeff in W.C.
    1988 R100 RT (the other woman)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  5. #5
    fracture
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    Quote Originally Posted by 88bmwJeff View Post
    Apart from the idle setting as indicated above, are you sure you have the idle mixture set properly? Those initial settings are just starting points, and need to be adjusted once the engine is warmed up.
    Forgot about that mixture screw. If it is in all the way the bike will run on the main circuit but not on the idle circuit. Of course, it could also be a bit too rich, that is, backed out too far.

    As stated, there are starting points that need to be adjusted when the engine is at normal temp. Run the mixture screw in all the way (do not use force, stop when you feel it will not turn anymore) and back out about 1/2 to 3/4 turn. That should be a good starting point for the mixture screw.

  6. #6
    Administrator 20774's Avatar
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    Quote Originally Posted by b52g View Post
    Installed new O rings,5 of them in each carb.
    Does this mean the throttle shaft o-rings, too? If the butterfly plates don't get centered properly, then you'll have uneven or incorrect flow at idle. Also, the plates have a beveled edge and that bevel must be right when the butterflies come back to rest.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    Registered User mneblett's Avatar
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    Quote Originally Posted by 20774 View Post
    Does this mean the throttle shaft o-rings, too? If the butterfly plates don't get centered properly, then you'll have uneven or incorrect flow at idle. Also, the plates have a beveled edge and that bevel must be right when the butterflies come back to rest.
    If the discs are improperly reinstalled, they won't seal the bore when fully closed. If that were the case here, I'd expect that he'd have the problem of too much idle speed -- but I am only speculating now; I've never had experience with a Bing with an incorrectly installed butterfly.

  8. #8
    Administrator 20774's Avatar
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    Quote Originally Posted by mneblett View Post
    If the discs are improperly reinstalled, they won't seal the bore when fully closed. If that were the case here, I'd expect that he'd have the problem of too much idle speed -- but I am only speculating now; I've never had experience with a Bing with an incorrectly installed butterfly.
    I don't have any direct experience either, but I offer it up. Seems to me without the proper seal, you'd be running lean because too much air is getting through, not being routed properly through the idle circuit. My logic...might be wrong...not the first time...or the last...!
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  9. #9
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    Here is what I found. Pulled left carb again and this time I noticed the choke cable, between the adjustment screw on the carb and where it connects with the choke lever also on the carb was very kinked. Found it had frayed. and some wickers were jammed up in between the cable and the rubber sheaf not allowing the choke lever on the carb to close, hence the flooding condition. Ordered new cables[plural] . Hopefully that will do the trick. Thanks for the advice, will inform you of the results
    I have met the enemy, and he is us
    2011 R 1200 RT
    1992R100RT
    2007 Roadstar Midnight Silverado

  10. #10
    Bill Burke
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    Quote Originally Posted by mneblett View Post
    If the discs are improperly reinstalled, they won't seal the bore when fully closed. If that were the case here, I'd expect that he'd have the problem of too much idle speed -- but I am only speculating now; I've never had experience with a Bing with an incorrectly installed butterfly.
    Quite right. I was baffled for years with a mixture screw that could be completely closed on a carb and the engine would continue to idle on that side. And idle was generally unstable over the years and would almost always drift high (unless it was just a routine valve adjustment). After doing all the other checks (vacuum leaks, cable kinks, enrichener not closed) I finally examined the butterfly and noticed it didn't seat squarely leaving too much daylight. I loosened the two screws securing the butterfly plate to the butterfly shaft, recentered the plate and torqued the screws down. Problem finally solved.

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