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  1. #1

    Carb Issue - Need Help

    I am having trouble correcting a high idle issue.

    I have two nearly identical 2000 XL700s with dual SBN 38 carbs. I rebuilt the engines and carbs (gasket, soft parts) last winter and the skis ran pretty well over the summer. Put about 40 hours on each last year. The only issues I had were occasional hard starting and one of the skis has a high idle (1400 rpm) that I could not drop to spec (1200 rpm) even by backing out the idle speed screw totally. This made it char to comply in ‘no WAVE’ zones.

    I’m pulling off the chokes and adding primers to solve the starting problem (spraying gas in the carbs worked well last year), but I can’t figure out how to fix the idle problem. Pulled and re-inspected the carbs last week and they are clean inside.

    The only difference I have observed is: 1 set of carbs has the pop-off at about 23 psi +/- 1 psi, and the high speed adjuster screws appear to be somewhat grooved (must have over-tightened, so I’m ordering replacements). The other set of carbs has a pop-off at about 48 psi +/- 1 psi.

    Unfortunately, I wasn’t smart enough to track which set of carbs was on which machine.

    Will the groves in the high speed screws affect the low speeded idle?
    Does anyone know what pop-off pressure I should be running? Is it possible that the main jet is opening at idle (presumably from the 23 psi set of carbs)?
    Other possibilities (there shouldn’t be any air leaks in piston/case assembly. Did leak tests as part of rebuilds)?

    I pre-mix, if that makes any difference.


  2. #2
    Moderator OsideBill's Avatar
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    The pop-off can affect idle speed, so can an air leak. The damaged adjustment needles can also cause problems.

    Read the attached manual it goes over the functions of the idle circuit. I would say you need to figure out what your jetting is and find out what is what to make the pop off different.
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  3. #3
    Quote Originally Posted by OsideBill View Post
    The pop-off can affect idle speed, so can an air leak. The damaged adjustment needles can also cause problems.

    Read the attached manual it goes over the functions of the idle circuit. I would say you need to figure out what your jetting is and find out what is what to make the pop off different.

    Wow, nice info Bill.

    Would you happen to have a PDF manual for the carbs on my 2001 GP1200R. I am green behind the ears and need to read up... Alot...

    Many thanks enlightened one.
    Last edited by barrettabney; 10-07-2009 at 10:55 AM. Reason: signature added

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