2002 YZ250f Hot starting problem!

Hello all,

I just got a 2002 YZ250f. The bike starts 1st or 2nd kick when cold. If I let a buddy ride that does not ride it hard the bike will start no problem anytime. If I get out on it and thrash it, the bike will not start for about 10 min. The bike never shuts off during the ride. It seems to be lean to me. The bike does not seem like it has enough pull at the top. I have been riding 2 strokes for about 11 years and this bike will not keep up with my procircuit kx 125. It also sounds like it is breaking up on the long straight aways on the top end. I have checked the valves and they are fine. I have done a leak down test on it and it is 3%. I am not sure what the book calls for but, this does not seem to bad to me. I checked the plug and it is lean (white). I went bigger one size on the main jet and that has not helped. I am just curious if anyone has any ideas on this problem. Does anyone know what the stock jetting & float level is for this bike? Any help would be greatly appreicated. Thanks in advance.


What exactly were the measurements on those valves?

Also, what is the current jetting (mj, pj, maj, paj, needle, clip position)? Any airbox mods? Stock exhaust or aftermarket?

If you are breaking up in the top, it's probably rich in the top end. I know it doesn't make sense but, if your bike is not revving out, it's rich. It could also be your ignition or spark plug cap. :cry:

I am having the same problem! i just checked my valves about 2 months ago and had to reshim the exhaust valves, still did not fix the problem. MODS: JD jet kit, blue #3, 180mj, 42pj, 40lj, ap squirt timed / adjusted, stock maj, zip-ty fuel screw (various settings), uni air filter with screen removed, new power now, and full white bros e-series exhaust with 12 discs installed.Oh yeah it's a 2002 yz250f and still has stock cam with manual decomp. Starts in 1-2 kicks when cold but very hard to start when warm. Any ideas? Thanks

Lower the main jet with the power-now (#175) and try lowering the float level ~2mm. When a rider hammers a bike harder the float level will rise, the same as rocking the bike forward/back when parked, which richens the jetting. Also, turn the idle mixture fuel screw inwards slightly. With the jetting kit, try running the leaner red marked needle in the middle clip position.


Thanks for the info, I will give it a try.

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