I'm brand new to this forum,and it looks like there are some very knowledgeable people out there.I need help with my bear tracker 250. I just changed the timing chain, and when I fire it up it revs like crazy and the head pipe glows red. I've set the crank at TDC, and made sure the cam and sprocket were lined up with the mark on the head. I've tried moving the sprocket one tooth each way to no avail. Is there anyone out there who has had this or a similar problem? Thanks for any help!

 

Welcome aboard!! Was cam chain making noise for the reason of replaciing cam chain? or jump time? or came off? need more infromation.... have you check value adjustments?

 

The Bear Tracker threw the chain when my daughter was warming it up. I re-instaled the old chain but the chain tensioner wasn't even making contact with the chain, so I ordered a new chain from Yamaha. Along with the over-reving , the spark plug looks like it's running very lean. I didn't completely disconnect the carb, but it sure looks suspect. I don't know anything about Mikuni carbs, but could this be part of the problem?

 

im having the exact same problem i though the manifold inlet boot was sucking air which it was...replaced.. i thought maybe the diaphram spring my be to weak thats why its over reving?? or a chipped valve? if you give it throttle it seems to idle for a bit before reving out again

 

I removed the carb, throughly cleaned all the jets and float bowl, checked for proper movement of the slide and needle, adjusted the throttle cable and now it runs almost fine. By almost fine I mean it will idle smooth for 30 sec. and then slowly increase RPM, not to blow up speed, just a few hundred RPMs. Could this indicate a vacuume leak? I checked all the connections, sprayed WD40 at the joints, didn't cause a rise in RPM, made sure the air filter is clean. It just does it when it is sitting and idling. Anyone have any suggestions?