2002 Yamaha TT-R 250 Logo
Posted on Oct 04, 2009
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I have a 1994 Yamaha TTR250, bike was running fine but all of a sudden developed a misfire. Engine will start but misfires and will not get full revs. When I open the throttle the revs try and increase but engine is misfiring all the time and the revs do not even get to half it used to. I have stripped the cab and cleaned pilot/main and needle jets. Air intake is all good. Checked electrical checks as per the yamaha manual (coil, wiring, pick-up coil resistance, kill switch, ign switch). Could this be the CDI unit Thanks in advance for any help

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Hey i have a ttr250 2000 model i had a very similar problem, it was misfiring and dropping out at high revs. i striped the carb cleaned everything out adjusted jet pins, oils, air/ fuel screw changed the spark plug nothing worked. in the end i got a can of carbi cleaner and sprayed it while the engine was running into the intake after alot of smoke coming out the exhaust. hey presto suddenly my bike works and revs fine. with a little bit of tuning good as new. so might be worth a try. I think it was from over oiling the air filter and the oil messing with the valves. hope this helps
aidan

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When the cam chain stretches beyond adjustment the cam on the exhaust side can skip over a tooth upon stalling the bike will still run but will have no power to speak of and if you keep playing and trying to start it it will skip another tooth then wont run if you keep playin it can eventually have the piston hit the valves and catastrophy .new cam chain .set valve timing correctely.fixed .no tuning carb or spark problems .

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Sounds like you did everything you could but it does sound like there's only one option left and that's the CDI
good going i"d like a response feedback on this if you got time,,,thanks.

  • Anonymous Oct 04, 2009

    I forgot that you had mentioned that you messed with the jet/pilot and needles did you insure that you put but all pieces exactly where they came from and when you installed the pilots did you know the exact amount of turns to set it to...when i had a problem similar to this it was the carbs on one of the bowls the#1 main jet fell off into the bowl...what did you use to clean it...because you shouldnt use auto carb cleaners there to corrosive to smaller rubber parts...if i was you i"d take it back off and get an really inspect the main jets and the correct settings of the needles. also back firing could mean a defective ignition component.you didnt mentions plugs yet, have they been replaced. try a can of Seaforam first before digging into this. $10 from autozone 1/4 can to two gallons and get on it right away next time you can get out there and ride. it a dirt bike right! it might take about 10 miles to cleanout the situation though. good luck

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