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I have a 2000 Yamaha big bear 400, I was riding it this mourning and all of the sudden, smoke raised fro the seat, I took that off and the smoke was coming from the air box, I took that off and there was a decent sized puddle of oil laying in the bottom, I checked the tube coming from the carburetor and it was coated in oil. I immediately stopped riding and towed it home. I asked family members and they said that I blew the motor. others said that I could have blew some rings on the pistons or even the spark plug fouled out. I took it out for less than a 5 minute ride and when I got back it was smoking again, although it didn't seem to have any loss in power and it ran fine. As of now I just need thoughts or ideas or anything that might help... I use this to haul wood for the winter and plow in the winter, yeah its a long time away but I NEED this fixed now!
 

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If it is running fine, then I would suspect an oil seal somewhere. Are you saying the oil in is the airbox?

If so, there are two ways it can get there... Through the carb, which would mean not only are your rings shot, but your valves are seating all the way. But it would run like crap if that was the case.

So the other possibility is oil is coming up through one of the vent tubes. If that is the case, then you may just have to much oil in it or you're not keeping the ATV right-side up. :D
 
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