yz426 problem

[hartwill]

Ok guys, I don't know what else to do here.. I have a yz426f that gives me no sign it even wants to run.. I know this was a pretty common hybrid that's why I'm posting here. I have done everything. I just had the valves done, checked the timing, thoroughly cleaned the carb, new plug, fresh gas, I even did the ritual yamaha starting dance and it doesn't even try to start. It's getting spark, fuel, air, and it has a ton of compression.. anyone have any ideas?

[C41Xracer]

Have you tried starting fluid to make sure it even fires?

[800screws]

have someone pull u....dont give it gas though! just pull it and let the clutch out...if it doesnt go that way something is wrong.

[C41Xracer]

Is the motor actually getting fuel? The reason I ask this I just went through a similar problem. It ended up being the float needle, it was hung up and not letting fuel into the bowl. Take the drain plug off of the bowl to see if theres fuel in there.

[87turbogn]

I had one of them once and you couldn't grind the valves because they were coated titanium. I had to replace them. Even though you have good compression, they still might not be seating. If you have a leak down tester, it would find any compression loss.....(valves). A dirty air filter hammers the intakes and if they don't seal perfectly, it won't fire. Is the cam timing marks lined up? I know you said you checked the timing. Cam or spark? Or both?

[hartwill]

I bought this last year from my friends dad, it only had 20hrs on it and would not run. When you kicked it over it was dragging a lot almost like a two stroke with a bad crank. We tore into it and the timing chain was really tight and thought because of this we couldn't kick it fast enough, so we fixed that and I took it to my local dealer to get the valves done and make sure the timing was good. I didn't put it all together before this to save on labor time. Got it home and put all together and nothing. Every once in a while it would POP or backfire but that's it. We pushed it kicked it threw wrenched at it gave up on it pleaded with it.. lol anything you can think of..

[C41Xracer]

sounds like the timing is off

[born2ride14]

Yea, check your timing

[87turbogn]

If it backfires, it still could be that the valves aren't sealing, especially the intakes. It'll pull in the fuel on the intake stroke and then under compression, it'll fire back out the intakes through the carb. So, when you said it backfires, is it thru the exhaust or the carb? Is it possible that when the dealer did the head, they got the lash too tight? I don't know what the spec is but I would think there would have to be a few thou.......

[hartwill]

I took it back to the dealer this morning. The said they would charge me $60 to tell me what's wrong with it. It would back fire through the carb though so maybe it is valves or timing which would be great because that's their fault.. we Will see what they come up with. Thanks guys for all your help..

[chronicsmoke]

Originally posted by hartwill
We pushed it kicked it threw wrenched at it gave up on it pleaded with it.. lol anything you can think of..


1. Try yelling at it

if that doesnt work,

2. Try spitting on it..

if that doesnt work, I'm all out of ideas:p

[JoePA]

the timing on them can be an SOB at times. Usualy when I do the valves in them it takes afew tries till I get the timing dead on. Did you replace the timing chain or reuse the old chain? If you used the old it may be streatched and causing the starting issues.

As others have mentioned put some gas down the plug hole or starting fluild. If you had the FCR carb apart and had the slide out make sure the front plate on the slide isn't upside down blocking off the pilot jet port...had this happen and the only way it would start is holding the throttle open a bit.

Give me a call tomorrow and we'll go over a few things.

[hartwill]

Well I got the 426 back today. I'm embarrased to say what the problem was.... Someone had the idle turned up way to high, and that's it.. starts up and runs perfect..lol