Help diagnosing YZ250R problem please!

[steveblaze4]

Hi, I own a 2003 yz250 2 stroke. I want to ride my bike again without it cutting out in 5th gear. It doesn't have to be 5th, it could be 4th too. Regardless, I have heard that it could be a handful of problems...but I don't know where to start. Any suggestions? It's obviously doing it at high RPM's and that makes me think it's a fuel problem.

I'm really close to pulling the motor out, (which I did about 5 rides ago to rebuild the top and bottom end), and replace the gasket between the top and bottom end. I think that it is pulling air in somewhere and that that could be where from.

Any other suggestions would be greatly appreciated. If I don't have to rip the motor apart I won't!

Thanks for any help.

P.S. I'm looking for a stock head off a 2003 YZ50R.

[BlueDiablo]

wait wait you dont have 5th grade or it just loses power? I would pull that motor out my guess is either tranny issues or of course the air leak. Possibly a crank seal.

[ONLY2STROKES]

does it only happen at full throttle?might be jetted rich.

[BlueDiablo]

More Info Would Help!

[steveblaze4]

I pulled the bike out of the garage and had some buddies listen to me do glory laps around the block. I guess in every gear it sounds like it is cutting out. It seems to pull just fine though, like there is no problem. When I hit top of 4th and into 5th the bike cuts out, like a jerking power loss. My buddy got on it and rode up the street and I heard how bad it sounded, and he said it felt fine too.
Crank seals is a possiblity sense it didn't do this before I rebuilt the motor(crank, bearings, seals, cylinder, and piston). It is damn frusterating whatever it is. Thanks for the replies.

[ONLY2STROKES]

does it act worse at wide open throttle?like its hitting a rev liniter?

[MX86]

i don't think the yz has a rev limiter... either that or i need to adjust my carb because i sure havn't hit it. sounds like you really need to replace the crank seals.. it's drawing in air on the up stroke and pushing out gas/air on the down stroke and sufficating the engine

[ONLY2STROKES]

ummm iwas trying to relate a too rich main jet to a (rev limiter).like he described its cuuting out...like hitting a rev limiter....possible rich jetting.

[MX86]

yeah it could be rich jetting, but i'm assuming since he's probably had the bike for a while that it couldn't be that but hey ya never know.