# GAS in the Oil



## Gillie (Dec 12, 2004)

Occasionally I would see this on various engines in my Shop. This post is so we can address a problem that will cause an engine, regardless of the type of oil system, to throw a rod, score the crank or put a hole in the crankcase.
Regardless of whether the gas is from gravity feed or diaphram or electric fuel pump. In order for gas to get to the cylinder it must go past the needle valve.

Gas will pass through the carb for one of the following reasons:

1. normal operation, the float drops and allows fuel to pass to the cylinder.

2. Engine stopped, dirt has held the needle off of the seat and fuel passes through. In this condition fuel will run until it empties the fuel tank in a gravity feed system. It will not empty the tank in a diaphram or electric system unless the diaphram and metering block are faulty and the fuel tank in located above the carbureator. I don't think the electric fuel pump will allow any fuel to pass, period, unless it is running for some reason. 
A bad float will also allow fuel to pass under the same conditions.

3. Float is out of adjustment
Engine running: Engine runs rich as evidensed by black exhaust smoke and that eye burning rich smell.
Engine stopped: Gas runs out of the carbureator and onto the ground or whatever is under the carb. Gravity feed system only.

Rhetorically, then how does gas get into the oil?
First, the intake valve on one of the cylinder has to be open.
Second, fuel has to be available. If the engine is running then it must be getting pushed into the crankcase by a cylinder that is not firing.
In the situation that I read in the email I recieved I would have to give it my best educated guess.

Curt stated that the engine would die when a plug wire from one of the cylinders was removed but not when the other was removed. (the not firing situation)

I had a Cub Cadet come into my shop that did pretty much the same thing. (18 hp Kohler)
The valve seat had come loose. (Kohler had a problem with this.)
It had fire but not much compression.

I think he may have a bad coil, plug wire or plug on the cylinder that isn't firing. 
I say this because he has good compression and it is even on both cylinders.

I think how the fuel is delivered in this situation is of no importance.


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