Where to go from here?

Take off the cover, and see if the mechanical ignition advancer will twist and then return to it's position.

If it sticks, lubrication with sewing machine oil or 3-in- one oil will help.

This advancer uses weights to control ignition advance/retard and needs periodic sevice.

mookieo2 wrote:

I would blip the throttle and it would rev to 4k and stay there for a while.

As per suggested, remove throttle cable from carbs.
Check to make sure you have NO AIR LEAKS. Anywhere in the entire intake track, from filter to exhaust tip.
Spray with WD40 around intakes, etc. Not exhaust, if there was a leak there it would be a loud cracking sound.

Check the cam chain tensioner to make sure its operating properly.
Make sure float levels in carbs are correct/same.

You can get more info on this stuff in the search here...

Cheers, good luck.

I think This is the problem I have. It started when it was at hot idle yesterday after I got it running pretty smooth. I wish the video still worked as I would like to verify the sound. I will check the advancer today, cam tensioner, then maybe try to sync the carbs if i get time.

Carb sync. might take a while, so I'd suggest getting a fan to keep the engine cool, otherwise overheating can result with damaged engine parts.