Question about 2004 Yamaha YZ 250 F

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Wont rev past 3/8 throttle!! I NEED HELP.

My 96 yz250 will run fine at lower rpm's but when u go over 3/8 throttle it acts like its hitting a rev limiter and bounces revs real quick....could this be my cdi box going bad?

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  • peter smith Dec 23, 2013

    it sounds more electrical than fuel mianly if it was happening in low revs it would be your idle jet which are very small if it was running alright before and not now the main jet is useally not a problem the jet is so large and it useally a problem if you change a exhaust or do a port and polish then it is a job to go for a larger jet size so it would not be that .i am sorry to say it does sound like a cdi or try another coil. hope this helps cheers pete

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Check your jetting in your carb. It seems like your idle jet is fine but your main jet may be plugged or the wrong size.
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Posted on Mar 15, 2013

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Could be. I had a 91 kx 250 that was acting crazy and it turned out to be the stator and cdi box. you can check the stator easly with a omes meter but the cdi box is nearly impossible to check. you pretty much have to buy a new one and try it. also check to see if your power valve is working.

Posted on Jan 22, 2009

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Posted on Jan 02, 2017

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SOURCE: MY YZ250 WONT REV PAST 3/8 THROTTLE. I NEED HELP!!

It does sound like an ignition timing problem, but could also be a breathing issue, air flow in or exhaust flow out could be restricted i.e.:dirty air filter, excessive carbon build up in exhaust pipe from burning too much oil or rich fuel mixture.
possibly and more likely some junk got into your fuel system and partially plugged up the main jet in the carb, -or has the needle on the slide been moved? The little circlip at the top of the needle, if it has one.
1.Replace the spark plug, check gap, check spark, it should be bright blue and fat.
2. check the fuel filter, if no filter check the carb for dirt.



Posted on Jan 20, 2009

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It does sound like an ignition timing problem, but could also be a breathing issue, air flow in or exhaust flow out could be restricted i.e.:dirty air filter, excessive carbon build up in exhaust pipe from burning too much oil or rich fuel mixture.
possibly and more likely some junk got into your fuel system and partially plugged up the main jet in the carb, -or has the needle on the slide been moved? The little circlip at the top of the needle, if it has one.
1.Replace the spark plug, check gap, check spark, it should be bright blue and fat.
2. check the fuel filter, if no filter check the carb for dirt.



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