Why is there Gas in my crankcase oil Yamaha FZR400 1WG?

yesterday when i had the bike running for less than 3 min the oil light came on and oil was spewing out the crankcase vent hose . So i drained the oil and to my suprise there was 3X the amount it should have and it smelt like gas. I would like to kno what is up with my Fizzer if anyone has any details i would love to hear them

First off you need to shut the petcock off when storing the bike. Secondly, the others are right, there is euther a hole or a piese of trash wedged in the seat. It MAY stay there or it MAY flush itselt out and never give any more problems. Just turn the fuel supply off for extended parking. for a few days and keep a check on the oil. Gas thins oil out and it WILL cause engine failure if not caught. Check it EVERY morning and evening!

wrong answer

Fuel in the crankcase comes form a weak seat.

Inside your carb there is a needle & seat valve.

If (A) dirt gets in there or (B) the seat gets worn

Fuel will leak past the needle, which is a shut of type deivce, and fill the piston area. Being that the gas is thinner than oil, it leaks past the rings into the crankcase.

Two things you can do, install a manual shut off

OR

get a new needle & seat

Draining the gas out of the float bowls may dislodge any debris that's keeping the float valve from closing ( if debris is the problem rather than a worn needle). Your petcock needs to be rebuilt if it is vacuum operated.
I had this problem with a couple of bikes, one filled the crankcase, and the other hydrolocked. I lucked out. In either case I could have been facing big time engine repair.

you need to go thru the carbs, you have worn out jets or a shot diaphragm. Either will let too much fuel go thru and if the motor cannot burn it, it dumps it and that would be into the crankcase. You could also have a clogged return line to the fuel tank and that once again would cause the motor to dump the excess into the motor. Good luck!