Yz400f

[jallenwalker]

Would it be possible to use a 426 head gasket on a 400? I ordered new gaskets for my 400 and they sen me a 95mm head gasket instead of a 92mm. Thanks in advance for any help!

[grayracer513]

Pretty certain that you can.  The 426 head fits your cylinder, so the gasket ought to be OK.  Check to see if it has adequate coverage of all the cooling ports, etc. 

[jallenwalker]

Yeah. Everything lines up great it's just the bore size is bigger. I had already put it on there but it won't start. I'm getting fuel fire compression and it's in time but I can't get the thing to start it also has a brand new plug in it. The compression won't rip your leg off or anything but it has plenty to run. The woodruff key was broke on it and I replaced it and now I'm back to square one. Lol I hate not being able to figure out an issue.

[grayracer513]

The key for the flywheel?  That will throw the ignition timing off, and if the cams were timed by using the misaligned flywheel, they need to be revisited. If you have a fresh plug, put it in.  Even a slightly fouled one can cause trouble.

 

The biggest thing that keeps the big YZF's from starting right, especially the old ones, is the carb.  Specifically, the pilot jet.  The jet may even appear to be open, but can have a dried film of varnish in the metering orifice that makes it too small to work. 

 

https://www.thumpertalk.com/topic/681801-bike-wont-start-dont-know-what-to-do/#entry6879695

[jallenwalker]

Yeah I put a new key in it and re-timed it. What happen originally was the tensioner went out in it an it jumped time so I bought a manual tensioner and put on it had it in time and nothing. Then took the flywheel off and noticed that so I replaced it. Still nothing. The bike was running fine prior to the tensioner problem the chain is in great shape too.

I will clean the carb again. It had some spots of varnish on the jets and around the bowl. But ran fine before. And only sat about 3 weeks whil I waited on parts. Thanks for all input. Much appreciated!!

[jallenwalker]

Plug was put in last night new outta the box. I don't think it would be fouled from the few times I've kicked it over but ya never know. It has a great spark to it still. I'm gonna start in it again in a few. I'll let ya know hat happens.

[brownz71]

I agree with gray. After weeks of trying to figure out why my 400 wouldn't start, I took a small needle and bent the end of it. Took the pilot jet out and stuck the needle in and brushed up against the sides. A massive amount of crud came out, and that's after soaking it in carb cleaner and visually seeing that it was Clear. Dang jets!

[jallenwalker]

Yeah I cleaned it again and it is starting now but will only run with the choke out and does as soon as I crack the throttle a little. But will idle forever as long as the choke is pulled on it. Would that be a dirty pilot circuit?

[grayracer513]

Normally, yes.  Also check the condition of the vacuum release plate on the engine side of the slide.  The "square" side goes down, not the rounded one, and there should be no cracks or missing corners.

[jallenwalker]

Okay thanks man. I really appreciate all the help. I will let ya know what happens after a good cleaning and the plate check.

[jallenwalker]

Okay new issue. And it probably has something to do with te previous one. The bike died while idling earlier so I pulled the plug and had no spark. Left the plug out and went back about 20 min later and had spark. What the hell is that about?!?!

[grayracer513]

If you can get it to fail again, test the stator and the ignition coil while it's hot.  One or the other, stator, most likely, may be opening up when heated.

[jallenwalker]

Okay thanks gray racer. I'll try that. This bike also caught on fire once and the coil got extremely hot/melted outside of it but it was still working so I never changed it. So it could be the coil is damaged.