carb help
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Thread: carb help

  1. #1
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    carb help

    I've just got a 97 yz250.
    I can get the bike started and it won't idle.
    I've cleaned the carbs out, main jet, pilot jet, and best I can the needle valve.
    I can't get the bowls off, as 2 of the philips screws head are stripping.

    If I remove the idle/choke assmebly, it idles fine.

    Help?...

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  3. #2
    Moderator Array TeeTee's Avatar
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    If the carbs needed cleaning then it's VERY likely that the stuff in the float bowl needs cleaning as well. The pilot jet lives in the float bowl so if you could not get it out then it didn't cleaned. I think you must mean the pilot or idle mix screw adjuster.

    And what do you mean "If I remove the idle/choke assmebly, it idles fine." Can you describe what parts these are and where on the carb they are with a bit of detail so we know what it really is?
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  4. #3
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    A little history, the bike sat for 14 months with fuel stabilized.
    I have drained the gas, and added fresh 40:1 gas.

    I did a bit more work today, and got the float bowls off.
    Upon inspection, the carb did not need cleaning. I did anyways, cause I had it appart.

    Even with the float bowls on, I can still access the jets, from top and bottom. I've pulled the pilot, and main jets. Cleaned them good.

    The idle/choke assembly of this Keihin PWM carb controls the is one unit. Pull it up to choke it, turn it to set the idle speed. With this unit out, it is sucking air. So I am thinking that my pilot is jetted way rich.

    Not sure if this helps,... here's the carb. http://www.keihin-us.com/am/products/pwm.php
    see the black thumbscrew, that's the idle/choke circuit.

    I am thinking about removing the Pilot air screw completely and leaving the choke circuit in. I think this should also lean out the circuit. Then it's off to the shop to get some smaller jets.

    Thoughts? think I am on the right track?

  5. #4
    Moderator Array TeeTee's Avatar
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    WOW! That is quite different. I'm just a hobbyist with this stuff so I don't get to see everything.

    Given what it is I don't doubt that it would suck air but that doesn't mean that there isn't problems in the carb.

    One thing I do with any carb clean is to use a spray can of carb cleaner and shoot it through any and all little passages that I can find. And most importantly make sure the stuff comes out somewhere else so I know the passages are not plugged.

    Do you know the history of this bike to know if it was running well before it was stored? If not then you can't really assume much since the previous owner may have been playing with jetting and screwed it up. Try to find the stock sizes for all the jets and return it to stock and work it up from there.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  6. #5
    mike was taken Array
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    Quote Originally Posted by TeeTee
    the previous owner may have been playing with jetting and screwed it up
    be careful, with a 4 stroke playing with the carbs might make it not run, with a 2 stroke you can make it seize a piston

  7. #6
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    Another test done today.
    Pulled the pilot air screw, and it idle fine.
    It is running 50/172 jets. stock is 48/170.

    since it is running when it's leaned out, off I go to buy smaller jets.

  8. #7
    Moderator Array TeeTee's Avatar
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    OK, if stock is only two sizes down but it requires totally removing the pilot screw to allow it to run then you obviously still have at least one blocked passage or other problem with the carb. A couple of numbers each on the pilot and main isn't going to produce anywhere near this level of trouble such that you need to let all that air leak in for it to run.

    I'd start with a re-clean and pay particular attention to using carb cleaner and compressed air to ensure that you blast out each and every little passage from both ends. And you'll want to pull as many parts out of the main body as possbile to check for stuff.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  9. #8
    Registered User Array J1k's Avatar
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    just keep in mind alot of newer 2 strokes rarely idle,the new ones anyway.some use the choke arm as a idle adjust as well.but i cant say for that bike for sure.Iam guessing it wont idle with the pwm carb.

    go to a stock pilot and the proper spark plug.set the airscrew to std stettings.i wouldt lean it out until you ride the bike and at least get a feel for the jetting.and a tad plug colour.

    like i said though do research it may not idle.just idle a bit then slowly die off and stall.not a bad thing in case ya crash.

  10. #9
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    darn, it's not the jet. Went down to a 48, and still the same problems.
    This is bugging the heck out of me.

    I've ripped this carb right apart. When I got to the nitty gritties today, there was some gel. Cleaned it all up.

    Would it be stange if a bike can't hold idle? I've never had a dirt bike before, but that seems really strange to me.

    Arghh!!!

  11. #10
    Moderator Array TeeTee's Avatar
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    It may well be a rough idle as John suggested but any bike should be able to idle in some manner even if it's ugly.

    If you found more gel'y goo then it stands to reason that there's a chance that there's still more in one of the little teeny passages. If it still isn't idling in some sort of manner then I'm betting on a plugged passage.

    Carb cleaner the shit out o' it and then stick it into a plastic bag to keep the cleaner from evaporating and let it sit for about an hour with the cleaner in there. Then hit each passage with compressed air from a gun with rubber tubing on the end so it seals well and blow out each passage from all ends. Be sure the air comes out at least one other point. Some are intended to come out two places depending on the carb design.

    Detail work, it comes down to details.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  12. #11
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    well, after my last post, which was because I came inside in search of beer, cause I had it up to here.... I went back out to put the bike away. Gavei it one more kick,... and it started,....settled down,... and idle!!

    Mucked around with the pilot air screw, and now she's purring.

    Figures... must been one little thing in one of the passages that finally gave way. I am really not sure what. I had some wire in every pilot/idle circuit and was able to get it all the way through so I could 'dental floss' it.

    Well she's running well now. Just gotta watch the plugs for the 'signs'.

    thanks...

  13. #12
    Moderator Array TeeTee's Avatar
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    Great!

    I'll bet the gas in the carb finally dissolved whatever last plug was in there and let the air or gas flow like it is supposed to. Either way it's fixed. Go play now...
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

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