I'm new to the ATV world, but can't wait to catch up! That being said, I need some help. I acquired a Yamaha 350 4x4 from my father-in-law. It appears that the bike has been sitting for at least a year based on the deflated tires and spider webs. No worries, I like a challenge. Since getting the bike, I replaced the battery, the air and oil filters, the spark plug, the exhaust system and cleaned the hell out of the carb. I should mention, the entire bike was caked with mud. Now the bike starts just fine, but it sounds like it's about to explode. If it had a tachometer, I would guess it's running about 5,000 plus. Also, where the head meets the new exhaust, is turning cherry red. As soon as I kill it, talk about a backfire, it's louder than my 12 gauge. I've got the Haynes Manual and have attempted to adjust the air/fuel mixture and the throttle screw ... no help. I wonder if the engine is frozen (valves, pistons, rings shot) or if, after cleaning the carb, I re-jetted the carb improperly? Any suggestions are greatly appreciated because I don't want to pay the delaer an arm and a leg. Thanks.

 

sounds like it is a jetting problem. did you remove the carb off the bike when you serviced the machine? is the carb bolted and all plumbing tightened? did you get the throttle return spring(s) set properly? check the mixture and idle screw and make sure the throttle cable is not hung up on anything that might cause a wide open throttle. did you use a factory replacement exhaust system or is it an aftermarket bolt on? those also change your fuel ratio as well. you would have to rejet the carb anyway with an aftermarket exhaust system.

when i got my 99 big bear, it was not running. it had been left under a tree with all the carb plumbing off the bike, air filter box wide open, all the plastic off the bike and the carb barely sitting in the frame. i sent it to yamaha, and 600 bucks later, it got a new battery, compete carb overhaul, new spark plug, oil + filter change, replaced the throttle cable, new rear brake cable, new rear brakes, and the fuel tank steam cleaned and the fuel shutoff valve replaced.

600 bucks is not bad for that much work. i did get cut a couple of hours labor due to the fact they had a lazy *** service manager that was demoted during the time my atv was there. they had the goddamn thing 5 days shy of 3 months. he kept bumping major repairs for the fast and easy stuff. once my atv was on the bench, it was in my hands running like a top a week later. the only thing that kept me from trail riding it as soon as i got it was the metal insert for the air filter was back ordered. it came in a week later and i hit the muddy trails wide open.