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Thread: CT70 dies at idle after WOT

  1. #1
    ct70newb is offline 70cc
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    CT70 dies at idle after WOT

    Hey guys,

    When I run my CT70 at WOT for a minute or so and then come to stop at a red light or stop sign the bike will often die. It won't start up again for 1 or 2 minutes, but when it starts up everything runs great.

    Any ideas?

    My first thought is a bad coil. After that, I'm thinking fuel supply is not replenishing fast enough for WOT. I pulled the fuel hose and it has a decent flow, definitely not great though. These carbs don't take much fuel though, so I don't think thats it.

    I just replaced the gas cap with a new one from CHP, so I dont think a vacuum is the issue.

    Best,
    Adam

  2. #2
    racerx's Avatar
    racerx is offline Super Moderator
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    Classic symptoms of low fuel level inside the bowl. Since the pilot jet sits higher in the bowl than the main, the motor can run longer on the main jet than it can on the pilot, a fuel level drops ever further below spec.

    Things to look for: restricted fuel line (pinched or partially clogged), low float level, obstructed inlet needle/seat asm, restricted tank vent. Start with the easy stuff first...unscrew the cap and see if that makes a difference. If that's it, then the forehead you don't slap may be your own. I've run across a few brand new, OER, K0 caps with vents that won't switch "on" completely. A little razor blade surgery was needed to cure the problem. With a defective cap vent, the vendor who sold it irrelevant. Incorrect float setting and pinched fuel lines are more common, they also take more time & work to check/change.

    If you've R&Rd the tank recently, you may soon discover how easy it is to pinch a fuel hose upon re-installation.

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    if you do think the float level is the issue, there's pics of the float setup i've found to be adjusted correctly here. if it's not, ignore this post...

  4. #4
    ct70newb is offline 70cc
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    Hey guys,

    I bought these carbs from CHP and they are completely unmodified. Would they really come to my door with the wrong float level?

    Anyways, my current thought is fuel flow. I'm going to check that first. I just went on a 10 mile ride. I noticed that you have to ride for quite a long time at WOT to die at idle. It is probably just a minor fuel restriction. Could it be my fuel filter?

    Best,
    Adam

  5. #5
    lukelaw1 is offline 110cc
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    It could be your fuel filter clogging. Have you replaced the fuel line and flush the tank recently?? I have read that cjpayne had a problem with a new gas cap not venting properly so don't rule that out completely

  6. #6
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    Quote Originally Posted by ct70newb View Post
    ...I noticed that you have to ride for quite a long time at WOT to die at idle. It is probably just a minor fuel restriction. Could it be my fuel filter?

    Best,
    Adam
    it sounds like it could be a valve clearance issue at that point. even an engine with a tiny bit less compression than it should have will run WOT, but idling is a different story. i'd remove those caps on the head and check the clearance. if you can ride a 'long time at WOT' and the bike doesn't die or lean out, fuel starvation is probably not your issue. thats when the bike is delivering the most fuel into the carb throat.

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