Question about 2002 Yamaha TT-R 250

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I have a 2004 TTR250 and it has a flat spot. Carb is clean, low mileage, no air leaks, have increased pilot jet to recommended spec. Still no change. Decorked the exhaust with a slight expectation that it may get worse. It goes really well and had no other issues. It just won't cruise due to surging and and a flat spot when opened out. Any ideas would be great. Regards

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Might be an idea to check and or replace air filter, check flaps/seat base or a guard is not obstructing airbox intake mouth. Take note of the stock plug numbers/letters and get a replacement Iridium Power type plug for it. (should be DENSO or equivelent, IU27 with 0.7mm gap). They are 2-3 times more expensive, but more than worth it. I run them in my Suzi DR650RS duallie and my Yammy IT250J Enduro. Cheers

Posted on Apr 29, 2010


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ok, assuming you replaced the carb header and stator with aftermarket parts, then I would say you definitely have a jetting issue. that flat spot is coming from your engine starving for fuel. its taking the gas too long to get from the carb to the engine. you would fix this by adjusting the idle mixture on the carb. the first thing I would do is look for the fuel mixture screw on the carb. im not familiar with your specific model. but the screw is usually found facing down on the bottom of the carb, directly in front of the bowl. when you find it, turn it counter clockwise about 1/2 turn at a time until that flat spot fades away. if that doesnt work, then you will need to up the size of the pilot jet inside the carb. maybe 1 or 2 sizes would be enough. if you replaced the carb with a bigger carb, then you may not be able to fix this problem. in my experience, larger carbs will increase power, but usually throttle response, especially low end, suffers considerably. the reason for this is lower intake velocity and vacuum. basically, with a bigger carb it takes a second longer for the fuel to be drawn from the carb and properly atomize with the air. hope this helps.if I overlooked anything let me know! some more info on the engine/modifications and carb/jet sizes would help too. good luck.

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