Fuel Draining in to Crankcase

[Lord Mort]

Hello,

I was looking for some suggestions on how to resolve this problem.

The fuel on my riding lawn mower is draining in to the crankcase. The engine runs perfectly (when the oil isn't diluted) so I'm inclined to think the block and intake gaskets are fine.

I just replaced the carb as I was told it was most likely vapor locked... That was not the issue.

Any ideas?

The mower is a crafstman 917.271012 and has a 15HP Kohler Engine.

Thanks!

 

[reynoldston]

I know you said you replaced the carburetor, Sounds like a float or needle valve problem. Only way the fuel can go into the crankcase is through the carburetor or a fuel pump.

 

[Mikel1]

Any debris/dirt in fuel tank? Also what are your engine #'s?

 

[Lord Mort]

I know you said you replaced the carburetor, Sounds like a float or needle valve problem. Only way the fuel can go into the crankcase is through the carburetor or a fuel pump.

I tried cleaning the carb before I replaced it. I put a brand new carb on, not just rebuilt so I doubt anything is sticking. I think you are on to something with the fuel pump. It appears to be a mechanical pump. It is bolted to the engine block and is almost immediately below the fuel tank.

I think I need to pull that thing off and see what is going on. I've never done that before so I'm not sure what to expect. Should there be a diaphragm or a check valve?

Mikel1, I replaced all the fuel lines when I did the carb so I cleaned the tank out while I was at it. The engine, according to Sears is "Kohler Engine model #CV15.5S-41596"
http://www.searspartsdirect.com/par...roducts-Parts/model-CV155S-41596/0598/1503500

 

[Mower Doctor 78006]

Even if you are using a new carb...... If your not running a good fuel filter, or the new carb's needle and seat arn't sealing it will flood the crankcase. Your fuel pump only runs when the engine is running. Ie doesn't flow fuel when engines off.

 

[redmondjp]

Install a fuel shutoff valve in the line between the tank and the carb and be done with it. This problem is so common that I have installed shutoff valves on three different neighbor's lawn tractors because they have all experienced the same problem. And if you don't get enough of the gasoline out of the crankcase after this happens, you can kiss the rod bearing goodbye within a few hours' of use (BTDT, have saved the pieces).

Back in the 'old days', every piece of equipment that had the fuel tank mounted above the carb had a shutoff valve on it. The only reason mfgrs. don't put one on now is because of cost-cutting.

There is a Briggs & Stratton p/n 698181 that has the inlet/outlet at right angles, or the B&S p/n 698183 for straight inline use. These are available for under $10 online and I buy them by the half-dozen.

 

[jsm0960]

Install a fuel shutoff valve in the line between the tank and the carb and be done with it. This problem is so common that I have installed shutoff valves on three different neighbor's lawn tractors because they have all experienced the same problem. And if you don't get enough of the gasoline out of the crankcase after this happens, you can kiss the rod bearing goodbye within a few hours' of use (BTDT, have saved the pieces).

Back in the 'old days', every piece of equipment that had the fuel tank mounted above the carb had a shutoff valve on it. The only reason mfgrs. don't put one on now is because of cost-cutting.

There is a Briggs & Stratton p/n 698181 that has the inlet/outlet at right angles, or the B&S p/n 698183 for straight inline use. These are available for under $10 online and I buy them by the half-dozen.

My thoughts exactly. I've seen this problem with Briggs and Kohler engines and with fuel shut off solenoid. After messing with carbs and solenoids the only real fix was to put a shut off valve on it.

 

[Lord Mort]

I did do that. As a matter of fact, it was the very first thing I tried. While it does slow the problem, it still happens after a couple of hours of run time.

 

[Lord Mort]

Even if you are using a new carb...... If your not running a good fuel filter, or the new carb's needle and seat arn't sealing it will flood the crankcase. Your fuel pump only runs when the engine is running. Ie doesn't flow fuel when engines off.

How does the fuel pump work though? There has to be some mechanical shaft or impeller that is driven by some sort of rod or armature... This would require a shaft seal or maybe some type of diaphragm right?

If that were to start leaking it could explain all my symptoms couldn't it? (this is just my logical train of thought) But when I look at this diagram, I get a bit confused...
http://c.searspartsdirect.com/lis_png/PLDM/10052849-00006.png

 

[redmondjp]

I did do that. As a matter of fact, it was the very first thing I tried. While it does slow the problem, it still happens after a couple of hours of run time.

So you're saying that this problem still happens while the engine is running? You've got a bad fuel pump then.

The fuel pump has a thin diaphragm in it - it uses crankcase pressure pulses to move the diaphragm, on the opposite side of which is the liquid fuel (and check valves) that is pumped. When the diaphragm leaks, fuel will go directly into the crankcase. If you had that much fuel running into the engine via the carb, it wouldn't even run due to a too-rich air-fuel mixture.

Sorry that I didn't understand your situation originally.