Need some Help, PLEASE...

OK, I know this probably has been covered a thousand times but I cn't really find help for my specific situation....Really it's a buddy of mine who needs help. He has a 02 wr250f that he has done most of the free mods to - grey wire cut, throttle stop cut, airbox cover removed. He has not done the BK mod but he wanted to try the YZ timing mod...So we did - And things went smoothly it doesn't want to run. It started at first after several kicks and ran rough then stalled...since then it just won't fire off..I am assuming it's a jetting problem (too Rich, right?)but what specifically needs adjusting? Just the pilot screw or does it need a new pilot jet? Or is it the clip that needs adjusting..Or maybe both?? Kind of confused on where to start...can someone help.....Oh he already has gone to a 175 MAIN (which shouldn't afect starting, right?)jet since he added a white Bros exhaust. We are in Virginia - around sea level. I'm really interested in this too because I have heard so much about it and I might try it on my 01 wr426...sorry for the long messege and THANKS for the help!!!

No, it's probably not jetting. Before going any further, recheck the valve timing. Pull two plugs on left side of crankcase and position at the I (not the H) on the flywheel at the timing window. Then pull the valve cover (two hoses and two 5mm allen bolts). First, the chain should be tight, pretty damn tight. Second, the intake sprocket should have the punch mark with the 'I' on it aligned almost exactly at the top of the head. Then, with YZ timing, the top punch mark on the exhaust sprocket should be in the 12th chain hole over from the top punch mark on the intake sprocket. Finally, the 'E' punchmark on the exhaust sprocket should be about 1 tooth above the level of the top of the head.

Good luck,


Check your spark plug.


Thanks guys,

We are going to recheck everything tonight before we try anything else but I can say that it definately fouled the plug. It was black and moist. If everything checks out as far as the timing then what?? Jetting?? Which way should we start?? Leaner on the pilot circuit or just the needle clip position? Or both?? Trying to get a idea because we are planning a trip with some other buddies for Sunday and would like to get this ironed out...Thanks again for the HELP!!


I just did the YZ timing on my 400, and no jetting changes were REQUIRED to make it run. I do plan on leaning out the bike, but I think you might be chasing a differnt issue.

Personally, I would turn my idle-adjust screw counter clockwise a couple of turns and try to fire it up. Get it running (probably at a high RPM) and them back it back down to where you want to be.

I'd make it run with the YZ timing prior to making any more modifications. That way, you have a better idea of what you are dealing with.

Good luck! I think the YZ timing is well worth the time.


Well...the problem was in the timing as you guys suggested. We had not noticed that the crank rotated from TDC while we were adjusting the exhaust cam. I never really thought about it but with the timing chain loose the weight of the piston/crank made things slip a couple of teeth on the intake cam side while we were fooling with the trying to move the exhaust cam clockwise one tooth. Now it is right and it started and ran fine. Haven't had a chance to really ride it and see how she runs.

I do have one more question though. Is it just me or are the instruction's on Motoman's website incorect about the position of the punch marks on the exhaust cam side. Can someone confirm thi? It was confusing the heck out of me but Mark your instrcutions seem to make sense after looking at the stock timing config. in the manual. Your instructions advance the exhaust cam one tooth clockwise putting the top punch mark in the 12 o'clock position not the 1 o'clock position as Motoman states. Could be just me's been a long day...

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