Gz250 gasoline fills the Air filter
 

I finally got my bike running.

I had the engine replaced last year, the old one was hard to start.

The guy took a long time fixing it, so I didn't get it back until the summer was over and the first cold front came in. It was too cold for me to ride until spring. Then I found the choke cable was frozen. It took two attempts to get the right part, now it was June. I started her up she ran great I took a ride around a few blocks. She ran great I was happy.

Today I went to go for a ride she started, but ran rough, then I saw fuel pouring out just above the chain. I removed the air filter, It was full of gasoline. I siphoned out and poured out the gas until the canister was empty and started her up. Gasoline was being pumped into the air filter canister through a hose from the crank case.

What could the problem be? Bad rings? blown gasket?

First, check to make sure your petcock is turned to the on position and not prime. In the prime mode, the fuel will flow freely into and out of the carb and into the air box.

Attachment 1125
Do you mean the one labeled "6" here, the breather hose?

If you are getting gasoline through hose number 6, it is coming from the crankcase into your air box. It is a breather tube only. Your carburetor is dumping fuel into the engine when it is turned off and parked. You never answered my question as to which position you have your fuel petcock turned to. If it is the original petcock, it will have 3 positions. Turning the long end of the selector to the 9 o'clock position is the on position. In that position, no fuel should flow to the carburetor until you turn the engine over and the vacuum from the carburetor pulls the fuel in. If the valve is turned straight down(prime), fuel will continually flow into the carburetor until it overflows and dumps fuel into your engine filling up the crankcase. The 3 o'clock position is your reserve setting.

Since I don't know your experience with bikes, I hope this is not sounding too condescending. If you left the petcock in the prime position, that would account for fuel in the crankcase and why it would then get pushed into the air box. You would then need to drain the oil/gas mixture out and put fresh oil and a new oil filter in. Never put more that a quart and a half in.

The only other possibility is that your float is stuck and letting fuel bypass into the engine through the jets that I am aware of, but then you would probably not get enough into the crankcase to fill it to the point that it is blowing it into your air box.

Let me know what you find. You will definitely need to drain the oil/gas out though.

Ours did this.

Your float is sticking open. Even with the petcock on Prime, the petcock is SUPPOSED to close and stop fuel flow. If it sticks open, then fuel will overflow the bowl, flow into the carb throat and down into the bottom of the airbox. Once the fuel gets high enough inside the airbox, gas will then run down into your crank case.

I HIGHLY recommend you drain your oil ASAP and be alert for fuel. I ended up with about two gallons of fuel in the engine case.

Let me clarify something here for all GZ250 users.
GZ250 was designed to have safety redundancy preventing gasoline overflow into engine (most motorcycles do). Both petcock and carburetor needle valve operated by float have to fail before fuel overflow occurs. So if you have fuel in airbox or in oil you need to fix two separate issues:
1. You need to rebuild your petcock (or better yet - replace with manual one).
2. You need to take carburetor apart and make sure that float is good and valve it closes has good seal (both needle in the seat and seat in the carb body). Float needs to be adjusted so when needle valve closes (not carb upside down - service manual is actually wrong here) lowest part of float is 13 mm from bowl seal surface). Carburetor upside down causes float to not only close the valve but also collapse vibration dampening/overload spring inside the needle. Adjusting float with carb positioned upside down will result in fuel level too low.
Starting and running engine with both petcock and carb float needle valve leaking, is the best way to cause catastrophic engine failure. You may hydro lock the engine or cause to run it without lubrication - both not a good thing.
I recently noticed my engine getting hard to start if seating for just few minutes (would flood and need long crank with fully opened throttle). I have manual petcock and always close it for parking. Took carb apart - needle was good. Took seat out of carb body and oring around it was completely deteriorated. It was allowing gas flow around valve to fill bowl regardless of the float valve. It was happening fast enough that stopping engine for fill up at the gas station would end up flooding it. Leaving overnight could result in filling crank case and air box completely.