1992 Yamaha Big Bear Troubles...Please Help

[lindo1951]

Hi everyone. I have a 1992 Big Bear 4x4 that is giving me grief. About a week ago I had the bike running but the idle was very slow. So I adjusted the idle screw and then the bike shut off. I fooled with the screw for a couple of days but it still would not start.

So today I changed the spark plug and took the carburetor off the bike. I cleaned it all up and put it back on the bike. The bike fired up after a couple hits of the starter button and I was very happy. I let it run for a few minutes and it sounded great. I then jumped on the bike and moved it about 20 feet and stopped. The bike still idled away but was a little slow again. I turned up the idle screw a little and the idle speed increased to a good pace. I then went to move the bike again and it started to make sort of a cracking or pinging sound and shut off. Now it will not start again. I should add that it had made those sounds a few times before the bike died the first time on me. WHAT DO I DO!!!!! It is driving me crazy. I hope that someone out there can help me out.

Thanks to all in advance.

Steve

[DirtDemon]

I would start by checking things like vavle clearance, compression, make sure you have a good plug and a clean air filter. If it has been sitting for a while, you might drain the fuel and put new gas in it. Also, when you cleaned the carb, did you take it completely apart and clean every hole, and make sure the jets were clear? I would run through all of these things, your problems could be related to any of them. Good luck.

[lindo1951]

Thanks for you're response. It has clean gas, a new plug, and the air filter is fine. I will check the other things that you suggested. Thanks again.

[Raptor8]

timing chain would have to be pretty whipped to do that, but it's possible. I agree I think you should start at the valve adjustments- it is often neglected. check your book for how to adjust the timing chain. most Yammers have the adjuster sticking out of the back, under the carb. you'll need a book to adjust it correctly.

if the chain is loose enuf to rub against something and make noise, then your valve timing is all over the place and that could easily be your slow idle- retarded timing. It's usually a simple procedure but check out a book first.

[Raptor8]

the cracking/pinging sound worries me, and the idle up. it could be valves hitting the piston- not good!

weird idle adjustment could be slack in that timing chain and that could let the valves smack the piston crown. I'll think on it some more.

Swing by Harbor freight and buy an automotive stethoscope- cheap and many uses- including scaring your friends! If not, use a long screwdriver. start it up and put the screwdriver in various places on the engine, put your ear aginst it and see if you can isolate where the sound is coming from. that could tell us a lot.

Edited March 18, 2011 by Raptor8