81 yt 125 help

[Mangelcc]

I have a yt 125 that was up until yesterday running great. Today she started smoking like a freight train. This bike has been in storage for a long time. Been back runnings for 6 months. Got out of storage took apart top end, honed,replaced piston and rings and gasket set. Changed tran oil and premix oil for oil pump. Cylinder was in great shape could still see light cross hatches. Compression is 105-110 psi. Still using factory oil pump, cleaned carb, still smokes bad. Is it possible to be crank seal? inside carb appears wet, leaking into air box. it is not leaking out overflow tube. maybe to much gas leaking into carb. air mixture screw set at 1 1/2 turns out. Any ideas??? Thanks

[stump3r12]

I also have an 81 yt125 and i have a similar problem. First thing to check and see is if you are just burning extra oil (make sure that your pump is not running abnormally, even though Yamaha is really good for their mixing) next thing to check is if your carb overflow is plugged. But i found that it was most commonly caused by the carbon and oil caught in the spark arrestor. My machine used to run rich and that caused a big excess of junk in the exhaust. So it could be just the excess oil that is burning off, especially if it has been sitting for a long time.

[Mangelcc]

Is there a way to check and clean exhaust if it has excess oil in it???? over flow tube is clean. been running really good all of a sudden started smoking bad more i got on it the worse it got. Thanks.

[RubberSalt]

The exhaust on the 175 has a drain plug, i imagine the 125 has 1 also. Try removing that and running it around for a while.

Assuming you haven't changed to a new type of oil;

Clean the carb - if that don't fix it then try and bypass the oil injection and do a premix of 32:1. If it still smokes horrible do a leak down and check the crank seals.

[Mangelcc]

pulled head off and pulled the pull start a couple of times and found oil coming past rings in one spot. cylinder still had cross hatches all along but in that spot. Like the rings did not seat correctly. still had 100 psi compression. trans oil smelt like gas and was thin. what next???????????

[RubberSalt]

Replace your crank seal on the trans side, it's leaking. I'd go ahead and replace the seal on the flywheel side also. Odds are that it's shot also, or on it's last legs.

After that, reassemble and perform a leak down on the engine, make sure it does not leak.

[Mangelcc]

I took head off and sent to machine shop. Said cylinder was out of round. Ordered a 56.5mm wiseco piston and new rings going to have the cylinder bored out. Im also going to get a carb kit if i can find one, new air filter, both side crank seals. That should cover it. Thanks for reply.