timing issue...

[Flatlander]

1986 250r, runs great for about 15 minutes, then fouls the sparkplug.
I have been told it might be a timing issue. I have tried two different carbs, and it runs the same on either one.
I was wondering if anyone else has had this same problem, or if anyone knows how to fix the problem?
If it is a timing issue how do you correct the timing?

[GPracer2500]

You can check the ignition timing with a timing light. I doubt that's it though. I'd guess poor jetting or a leaky clutch side crank seal is letting tranny fluid into the cylinder.

[adam833]

check the flywheel, I had a similar problem, it would run for a few min with a stock carb and then a brand new carb and then foul the plugs. Turned out my flywheel was messed up and messing up the timing, gave me tons of kickback too. Bought a ricky stator flywheel for 125.00 and rejetted and it runs excellent now..
see my post
http://www.exriders.com/vbb/showthread.php?s=&threadid=334390

[chawness]

I'll put my money on jetting.

[Iliketogofast]

Timing is controlled by the longest port on the intake side. If you think of it as a four stroke, the longer that big skinny port is the longer the valves stay open and the more fuel/air mix gets let in. Ignition timing is controlled (I believe) by the stator.

That being said, I don't think it's a timing issue. It's likely a jetting problem. Go a little leaner on the main jet and if that doesn't fix your problem then go a little leaner on the needle as well.

[speedfreek]

Mine did the same thing. It was the stator. A mechanic even ohmed it out and it checked out fine so I replaced EVERYTHING even rebuilt the engine. Decided to send stator off to be re-wound and that fixed it!

[Dave83]

It could be electrical.You didnt say wether it just started doing this or not.If the bike has always ran on the current jetting you need to get it warm and then go thru the electrical check list with an ohm meter.Its possible that the windings in the stator are expanding and causing problems or even the coil is getting warm and it s internals are gapping open.Something else to look at is the carrier for the counter balance bearing.They will crack right behind where the pickup coil bolts on.I fought this for 6 months before I found mine was broke.