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1987 Yamaha big bear 350 is smoking, need help

Duckin

By Duckin
in Yamaha ATV Forum

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Duckin Newbie

Duckin

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I have got a 87 big bear 350 4x4, I have been working on.It was running rough when I bought it.I cleaned the carbs and need to adjust it a little more to get it right,but it is running better. But, the problem I have it smokes alot,when I bought it and got it home it was low on oil and did not smoke much,but after I added the proper amount of oil it smokes alot.It is white colored smoke and it has oil residue on the tail pipe,it seems to have good compression. Do I need new rings or valve seals or guides?

Any help would be appreciated.

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DirtDemon Veteran

DirtDemon

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If there is oil in the airbox, then your problem may just be a crankcase venting issue, or maybe you just put too much oil in. If there is no sign of oil in the airbox, then your problem is inside the motor and the only way to figure out exactly what it is will be to take the motor apart. It could be valve guides or seals, it could be piston/rings or worn cylinder walls, it could be a blown gasket. Also, there is an o-ring that sits under a collar that goes between the cylinder and crankcase this is to seal off the oil that runs through to the cylinder head. There is also a gasket that goes between the cylinder and the head, it sits inside the a large cutout on the head gasket, this is also to seal off the oil that passes through from the crankcase to the head. If either the o-ring or gasket is bad, then this oil will run into the cylinder. I would strongly suggest purchasing a repair manual.

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