Crankcase Vent hose on used bike

[KDXDan]

I was checking out a used 99 yz 125 the other day and noticed that when the kid started the bike you could see smoke coming from the crankcase vent breather tube. Is this normal? I never noticed it on any of my other bikes. Could it be the rings are shot?

 

[Okiewan]

When "99 YZ" is in the subject, first line of the post, you can assume the post goes in the CR/KX/RM/YZ Forum.
Moved.

 

[KamikaziRida]

I would like to know also, it does that on my '94 Rm125, but I do think it is normal.

 

[fatty_k]

The breather hose you guys are talking about is not the crankcase breather hose, if your crankcase had a breather hose, the bike wouldn't run (hence 2 stroke). It is the transmission brether hose. If it is smoking, maybe some tranny oil is buring due to some sort of heat problem. If the top end is shot, that has nothing to do with the breather hose smoking.

 

[KDXDan]

fatty_k,
Could it be that the seal between the tranny and the crankcase is shot and the compression is pushing the burned air/fuel out the breather?

 

[fatty_k]

I belive that there is no seal between the crankcase and the tranny. I think it is just a bulkhead in there. So the tranny and crankcase are totally seperate compartmets seperated by a wall. Maybe someone else can answer that correctly.

 

[1999RM125]

are you sure it was the crank case hose? was it at the front of the motor, becasue im pretty sure if it was then it would be the power valve vent, and mine and all my friends bikes smoke a little bit from there

 

[scud1]

Yes there is a seal between the crank and the gearbox. If that seal was shot it would suck oil from the tranny not blow the opposite way.I cant see how the gear oil could be burning thru the vent hose though