Why does this YFZ450 Blow oil out of the overflow?

[dericsdad]

Anyone ever have this problem? A friend of mine's kid races an '05 YFZ450 and it is blowing oil out all over from the overflow catch can. The breather hose isn't hooked up to the airbox, but wasn't last year either. Oil level is correct. It blew oil out all over the back of the quad...

As far as we know, the only mod to the engine is a high compression piston.

[desertrider2121]

check the valve cover gasket. Same thing happened to mine and that was the problem

[BakerRacing40]

crank case vent pumping oil = worn rings

that's my bet on it

[wgw11]

I was having the same problem on sunday at my race nd didnt get to race my second moto but when I started it and rode it today it ran fine and didn't blow any oil out..what do you think caused it?

[younggun95]

Running on or near the rev limiter can cause it

[dericsdad]

Might have been overful...

[desertrider2121]

sorry i thought you were talking about the hole in the head by the spark plug.
but yeah possibly because of worn rings mine was doing that on a ride i was on but i ended up needing to get towed back. i cracked a piston so i fixed that then i put some fuel line and a vent on the other side of the fuel line because it makes it alot easier for dirt and dust to get in your motor