tried everything listed and nothing. Could something in the wiring / safety switches? I just don't know its out of my pay grade. Thanks for all the great advice anything else yall can think off please let me know. Thank you. David

 

You have already stated you have good spark....are you sure? If there is spark it should pop even if it desnt run. Should have a good blue spark capable of humping an 1/8" gap! If spark is yellow then it is weak. A shot of starting fluid should make it pop a couple times, if no ooo then no spark. Check your timing?? If plug fires out of sequence it may not pop. Did you check compression?? With a gage?

 

sorry no compression gauge but if you hold your thumb over the plug hole it has a lot of pressure. How do you check or adjust the timing? The spark is a dark blue and bright. How about the a valve adjustment? Is there a good video for that? Thanks again sorry to be a bother. David

 

First you need to beg, borrow or steal a compression gage, just holding your thumb over the hole means nothing! Your thumb will never hold 110 psi plus in pressure and that is the minium you need to make it run. You should seriously consider getting a factory service manual.

 

Back to drawing board. Located a compression gauge I'm picking it up on Monday. But I did squirt gas in the spark plug hole and nothing but getting nice blue spark at the plug. Is there a way to test the spark to make sure it's strong enough? I'm starting to think the motor is shot. But I'm no mechanic but I just don't understand what could be going on. Thanks again yall have be so helpful. Thank you. David

 

Like I wrote earlier, if the compression is OK, over 90psi, clean the carb out. There was a problem in it or it wouldn't have been peeing out. With a bike that has been stood, you often get problems with dirt/water in the fuel tank coming down and blocking the carb. Once all those are eliminated, if it still won't start, you may have a problem with faulty valve or ignition timing, but one step at a time.

 

Been trying everything. Took off the inspection cover on the side and the timing chain is off. Now what do I do? Any ideas. Please help. David

 

When you say chain is off,,, whhat do you mean? Off location, off gears, ??? Take it apart and reset or replace the timming chain..

 

what I found was the sprocket on the top inspection opening the chain was off and hanging down loose from the top sprocket. What steps are necessary to put it back? This engine has been attempted to start a lot we Thought it was carburetor. From what I seen on YouTube this can be done following the right steps i just need to know the steps. And i was told it was running and just quit. If that helps. Can this be fixed maybe? Thank you David

 

Problem is chains don't just come off, there is a reason, usually it has stretched so much the adjuster is at it's limit, but a broken or seized adjuster can cause it. Or, of course, previous owner may have been poking about in the engine and not put it on properly. If it has stretched it will need replacing. Never done it on a 250, but new 350 Yam chains are a right pain in the backside to fit, as alternator, flywheel and balancer gears all have to come off. The balancer gears are very difficult to re-time on them too. It may also have bent valves due to the piston hitting them, what was compression like?