My yamaha 250f will crank right up then as im riding it, ut will cut off while in on the trail. sometimes it wont crank back up and have trouble strating it up..how do i fixs this????

sounds like a bad cdi or stator, yamahas are notorious for junk electrics that fail when hot, hope this helps

I recommend that you don't open the air box unless you put a bigger jet in it because if your ratios arent right you will blow it up real quick

Always assemble your engine at TDC on the compression stroke...

is this while its runnig or not, sometimes the cluctch wont engage while the bike is not runnig, but will engage when running. its common. if not they may just be stuck. did you drain the oil and have the plates exsposed to elements while the engine was out of the frame. open the clutch plate cover, check that they look fine. other than that if the clutch is hydrolic check for air in the system. and also the fluid level. good look.

Take out your spark plug, but plug it into the plug-wire. Let the bottom of it dangle against the head and try to kick it. If no spark, problem with that, if it sparks, you may have a cracked head or piston/rings problems. This will at least rule one thing out.

I would replace the Rectifier. Easy fix. Good luck

Hi,

If you haven't put a new, properly charged battery already, do so.

Good Luck and Let me know,

Obe

You have a ground not grounding could be the switch itself and it may be the voltage reducer to the coil.