Question about 2004 Yamaha YZ 250 F

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Yz 150f bogs when you give full throttle all at once

You can slowley roll the throttle all the way through and the bike will take the gas perfect, but if you floor it the bike bogs, like there is a dead spot. The bike starts easy and idols smooth, it also has plenty of power once you get it past the bog. I have changed the carb, head, and stator. Any sugestions please??

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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.

Posted on Sep 06, 2009

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