2001 YZ426 Won't Start


I rode my 2001 yz426 last weekend (7 days ago) and it ran fine. Tried starting it last night and it wouldn't start at all. Not even a sputter. This is odd because mine is one of the lucky 426's that is really easy to start. I have stock cams and use the stock de-compression lever. Normally there is a point in the piston stroke that i can't push past when using the kick start lever, then i use the decomp lever to get past that point and start it up. As it sits now i can kick the bike all the way through the piston stroke without ever using the decomp lever.

I'm going to tear into it today. I guess I just wanted to know where to start, and if anyone has any helpful tips. I've never done anything with a 4-stroke top-end. I am pretty handy with a wrench, and have done plenty of 2-stroke top ends (haven't we all :ride:) Thanks in advance, and please let me know if anyone knows what my problem may be, or if you see any flaws in my plan of attack.


check spark

Get valve cover off, check valve clearances (re-shim if out of spec)

start ordering a top-end kit if the valves look good.

should i replace the cam chain while doing the top end?

If you have spark, check the valves. I definatly would get a cam chain with a rebuild. I sounds to be something goofy though.

i really do hope it's something goofy! I'm gonna go out and grab some feeler gauges and get in there asap. maybe i'll find something easy :ride: one can only hope! I'm gonna check the de-comp too.

Ok, just got done checking the valves. First thing to note, the timing marks don't line up "exactly" as they look in the manual pictures. I've inserted two pictures of what i mean. The marks on the cam gears were lined up perfectly, but the mark on the crank gear looked to be a few degrees off counter-clockwise. Please let me know if this is how they are supposed to look.

I'll post my valve clearances last, as they might be completely wrong if the timing is off. Did my cam chain jump a tooth on the crank gear? Or is this normal?



Valve clearances from left to right as seated on the bike. The fact that the valves were all virtually the same leads me to believe that they could possibly be in spec and that my timing is off. Is that a possibility judging by the pictures above?

EXHAUST: both were at .005 in or .127mm

INTAKE: .076mm/.003 in .064mm/.0025 in .076mm/.003 in

bump, anyone got some tips?

sounds like timing is off and it jump a tooth or 2. retime it and then try to start it

The timing is usually inspected way-around : set the crank to the correct position and check the marks on the camshafts against the head. Than you(us) will see how much your timing is off.

Looks like it jumped time for sure, hopefully not enough to smack any valves.

I had a 99 00 with steel valves that suffered a cracked valve seat. The valves checked OK WRT clearance, but not much compression. I found the culprit by pulling the head off the bike and filling the intake / exhaust ports with contact cleaner and looking for fluid to seep past a valve on the combustion chamber side.

I say this because the piston and rings were fine. A piston kit may or may not be needed. The head had to come off anyway.

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