Yz250f running problem

Hi there I am new to the forum, my names Aaron.

I have a 2005 yz250f and it's not running right. The problem that I am having is that it will either cut out or it revs real high while riding. It will cut out on low revs when slowing down as if I'm stalling it but then the other times it is fine on low speed and revs up in the high revs while riding. I need a bit of help on what to do with the carb? I've got the carb off and I've cleaned it out and cleaned the jets out. I just need a bit of help before I rebuild it and put it all back together. Maybe I need to jet the carb? Rebuild it? I just don't know. I was looking at the Boyesen quick shot do you think this would help me or would I be wasting my time?

All input would be much greatful thanks guys

Confirm the throttle cables move freely and have a little play.


Buy a NEW pilot jet. Stop bother to clean it


Inspect the fuel screw and the spring/washer/oring. Reintall. Gently close, open to 1.75 turns. Get the bike hot, then fine adjust for a perfect idle.

Should I buy a new jet kit or just the pilot jet? What size pilot jet should I get? I'm going to buy a fuel mixture screw to make it easier because it's got the standard screw at the moment. Should I buy a carb rebuild kit?

Stock pilot, not sure if you have a 42 or a 45 in your bike.


Do not buy an alloy screw, only brass or stainless steel.

I was thinking of getting a moose racing fuel or a msr or pro circuit something along them lines? Are they ok? Maybe I would just have to buy a carb rebuild kit to get the jet sizes

Or even the R&D flex jet fuel screw

out of your list, only the R&D is satisfactory.

Scotts, Kientech, James Dean and Merge Racing also make good screws.



you do not need a reulid kit, you need just a OEM pilot (about $5)

How do I find out what size my pilot jet is?

How do I find out what size my pilot jet is?


By taking off the float bowl, removing it and looking at it.

And it will have the size written on? Sorry for all the dumb question

Yes, stamped on the side.

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