I posted this in the Honda forum but no one replyed so maybe the yamaha guys can figure it out.



I was just riding my 400ex around and it just shut off. When I went to start it, I heard the starter crank, but not the motor. When you crank the starter over, you can still feel some air coming out of the pipe. Any ideas? I'm thinking timing chain snapped or skipped a tooth, but why? My mods are in my profile, but I am clueless. The quad had the motor work done to it whenever I bought it so I do not know very much.

Thanks
warriorman

BTW: When I say I can still feel some air coming out of the pipe, There isn't much. It's barely any.

 

Well the air is the piston pushing the air through the exhaust. If it just dies like that i would suspect spark, did you pull a plug to check for spark yet? If you have spark then go after fuel, but i doubt that would be it. A fuel problem would most likely make the quad run bad then die.

 

maby you have very low compresion but enought to get some air out

 

Maybe, but that doesn't really help me figure out wats wrong with it. Thanks for the reply though.

I have replaced a cam in my warrior, but thats about it. Think if I got myself a shop manual, I could do it myself?

 

If you have air coming out the exhaust it's not the timing chain. Sounds like you burnt a hole in the pistonand you have very little compression. Take the plug out, put your finger over the hole and turn it over. If it doesn't pop your finger off or at least try then you have what I described. If there is good compression, check for spark and fuel etc.

 

Hmm...I dunno, cuz the guy I took it to last monday said it sounds like the timing chain skipped a tooth, and he hasn't even started working on it, so I am gettin it tomorrow and me and my buddy are gonna start workin on it.

 

defiantly not the timeing chain as wshrdskin says sounds like a hole in ye ooh piston. good luck to ya

 

I had a similar problem when I drove my 300ex, I was just driving normally and it stalled. I tried turning it over and faint air came out, I dropped an exhaust valve.

Pull the head off and check it out.

 

compression check is in order

 

Honda EX's week link is the timing chain, perhaps it stretched to the point where it bent or broke an exhaust valve.[img]i/expressions/face-icon-small-sad.gif[/img]