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1999yz400fRider429

my 99yz400f wont run with the choke off

10 posts in this topic

i have a 1999 yz400f that i just picked up for 1000 bucks and it was running rough, i cleaned out the carb and it helped but not much, it has a hi flow air filter but other than that it is stock, the problem is when i start it with the choke on it runs ok but backfires, when the choke is shut off it idles for a few seconds then dies, what could be the problem?

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Yep, I had a problem like that too. Ended up that there was dirt in fuel. Could also be water.

Start by cleaning out the carb, and draining the fuel tank if you find any dirt/water in the carb.

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On the slide in the carb there is a rubber gasket on the backfire plate...most likely this is the culprit! Replace the gasket and make sure the plate isn't cracked!

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i messed around with air jets and it runns 99% better but i had my buddy look at it and he noticed the accelerator pump leaks when i twist the throttle (not much) you think thats why it still bogs a little when i twist the throttle fast.

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Now you are talking about a different problem. When you say the AP leaks, where is the leak coming from?

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