Fuel leaking into crankcase?

[Mr Mower Man]

I have a customer with a Kawasaki powered ZTR (FH601V-JS06), and he's been noticing lately that his oil level is gradually rising every time he checks it before each use. He can't smell gas, but he doesn't know what else could be raising the oil level. I'm accustomed to seeing this with gravity fed carburetors, but this engine uses a fuel pump since the tank is under the seat. Do you suppose the fuel in the line between the fuel pump and carburetor is leaking through the fuel inlet valve after he shuts the engine off? But now that I think about it, I would think the gas would end up in the cylinder first, and he'd notice the increased compression due to a cylinder full of gas. But he didn't say anything about that. The only other thing I could think of is that there's something wrong with the fuel pump, and it's somehow leaking fuel into the crankcase through the impulse hose.

He hasn't actually brought me the mower to look at it. I'm just repeating what he's said, and he wanted me to ask someone at Kawasaki about it. But I thought I'd start here first. He's thinking about putting a manual shutoff valve in the fuel line next to the carburetor to see if that changes anything.

Any thoughts?

[bluemower]

the fuel pump is a likely cause. The fuel pump has developed a small internal leak in the diaphragm. The crankcase has lower pressure and the pulses draw fuel from the leaking diaphragm.
The engine is probably running slightly rich from the fuel fumes expelled from the breather tube.

[Arkie]

New fuel pump and add a inline fuel shutoff would be good.
If eq owner fails to turn off fuel petcock it's his fault, not yours.

I add manually operated inline fuel shutoff valve mainly for use during long term storage, but also use cutoffs on gravity fed systems that depend on only the carb float needle to prevent gas/oil thinning.

[bobodu]

Yep...leaking diaphragm making oil...