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Thread: Yet another carb question

  1. #1
    apriliaforum prov-nov
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    Yet another carb question

    I have a 28mm VHST carb on one of my rs's. Its running etc but will NOT idle. I have tried a lot of things but have no hair left on my head and willing to fork $$$ out to someone if they could dial it in, but I am in Cincinnati, Ohio. Has stock intake, Arrow Full exhaust, 28mm Dellorto VHST carb. It DOES still hesitate a little under 6-7k as well. But it will not idle no matter the engine temp or settings on idle control or fuel/air mixture.
    Suggestions welcome! My email is cincykid38@gmail.com in case people dont want to be bothered answering within the thread. ANY help woul dbe greatly appreciated. I've taken carb apart, cleaned, blown everything out etc. Shimmed the needle one click which actually seemed to help when running), but I have to hold the throttle slightly open to let it warm up and when pulling clutch in to come to a s top or she will just rpm down and die.

  2. #2
    apriliaforum prov-nov
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    How many RS125’s do you have? If you have access you to one of your other bikes why not swap the carb and see what if that resolves the idle issue. Have you considered the fuel valve (diaphram) at the bottom of the tank. Also check to ameliorate sure the needle in the carb isn’t bent. They bend surprising easy.

  3. #3
    apriliaforum expert mattology's Avatar
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    question 1: air leaks anywhere on the engine/intake ?

    question 2: is the idle screw turned up enough ?

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  4. #4
    apriliaforum prov-nov
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    Ironically when I had it apart, the tip of the needle WAS slightly bent on the very end. I want to order a new one but not sure what size it is. I'm at work now but will look I guess when I get home. I did try to straighten the end out.

  5. #5
    apriliaforum prov-nov
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    I had the same issue, with the bent needle. I never tried to start it with the bent needle. I noticed it cleaning the carb and replaced it. Had the local Aprilia dealer ordered one had it in a week. I can check the part number when I get home from work.
    Last edited by jpk; Yesterday at 08:15 AM.

  6. #6
    apriliaforum prov-nov
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    I'm just getting back to this. If you need to replace the stock carb needle (spillo Conico D53), the part number is 856102. Factory setting is second notch from the top with the circlip. I don't think the bike will run right if it's bent. I think the part cost was about $10-$15.

  7. #7
    apriliaforum prov-nov Kevlar's Avatar
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    Please don't ever try to straighten or use a damaged carb needle. It has to be perfectly straight, and you'll never get it straightened out well enough for the bike to run well. It has more precise mixture than, say, a lawn mower. Thanks for your cooperation, glad you found the problem, and sorry for your trouble.
    The Patriarch of the SuperNaked: '05 TF

    Aprilias formerly owned: '02 ETV 1000 Caponord, '00 650 Pegaso Cube, '04 RST 1000 Futura, '99 RS 50 (70)

  8. #8
    apriliaforum expert maddad's Avatar
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    Yes good answer those ones are pretty cheap straightening never really works and it kind of floats on the circlip pivot ,although I have made one in the past for a carb I could not get one for it had 2 separate tapers and took a bit of measuring .

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