it's dead

4 replies to this topic
  • cornbread

Posted June 28, 2002 - 09:16 PM


YZ400F Coming down a hill, sharp right turn, dies,
wont start.. Feels like com. lever is always pulled in. Kicks way to easy.. Also pinging sound at top dead center...

Bent Valve????? Please Help...

  • Bambislayer

Posted June 28, 2002 - 09:48 PM


could be a stuck valve and it could be stuck because it is bent. before you tear into it, check the decompression lever cable and make sure it is not binding. you may have to lube it like a clutch cable to get it free up. you can visually check this by looking at the decompression actuator on the cylinder head. it should move when the cable is pulled. it sounds like the decomp lever to me. my bro used to have an xr600 and its cable was not adjusted properly when we got it and whenever the bars were turned all the way to the left it would quit from a lack of compression. good luck.

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  • sirthumpalot

Posted June 28, 2002 - 10:08 AM


The pinging sound sounds bad. I'll bet it's the piston hitting a valve. If I were you I would pop off the tank and valve cover and take a look at the valves. I'll bet one is hung open OR your cam timing is off. Be sure you figure out what's going on before you take the head off because you need to know the cause of the problem before you fix anything. Once you find the cause I would personally send the head to a trusted machine shop and let them do the work on the head, then you can replace any other worn out parts yourself if you like. A machine shop will have the special tools and experience for doing head work and IMHO it's worth the money.

I doubt it's the comp release simply because I don't think the comp release can hold the valve open far enough to hit the piston. Someone correct me if I'm wrong.

  • acarter920

Posted June 28, 2002 - 03:19 PM


I know where you can get a 426 motor for $2200 :)

  • Guest_blatham489_*

Posted June 28, 2002 - 05:41 PM


I agree with the stuck/bent valve - I know from experience on my recent event with my '98 YZ400F. The comment about the decomp lever is also correct - it won't hold it open far enough open to hit the piston. Think about this for a second and you'll agree that Yamaha was probably smart enough to foresee the motor moving with the decomp lever pulled and designed it tolerate this situation. My experience with Mototech in New Hampshire (888-942-6686)was excellent. They did a very nice job at a very reasonable price. And yes, it is worth the money to have them do it. Taking the head off is relatively easy - get a manual, then ship them the head and let them do their thing. Good luck.

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