Small Engines (Lawn Mowers, etc.): Gas in oil reservoir, riding lawn mower, gravity fed

Question
Hi Marc:

I just moved my riding lawn mower and noticed an oil leak. Upon further observation, I notice that the gas tank was also empty. Oddly enough the oil level is full, but contaminated with gas.

Any clues to what maybe wrong? Will this be a major repair at a small engine shop ($)?

Thanks,

D

Answer
This isn't too bad of a problem.  It could be one of two things happening.  

1.  The needle and seat are not sealing and fuel is running into the engine and PCV tube filling the crankcase.  This can be caused by a worn needle and/or seat or dirt under the inlet needle.  It can also be caused by the float having a leak or the pivot pin not allowing it to move freely.  You can visually inspect the inlet needle...if it has a groove worn in it, it will need to be replaced.  If this doesn't correct it, you may need to replace the seat as well and I recommend you have a shop do this for you (if you want to try it yourself, let me know and I can give you the details on how to replace the seat).  If you find dirt under the inlet needle, you should clean the entire fuel system and replace the filter (so it doesn't happen again).  You should be able to shake the float and listen if it contains liquid....if so, you will need to replace it.  If the float doesn't move freely on the pivot pin, determine what is causing the problem and correct.

2.  If your engine has a fuel pump (as opposed to gravity fed fuel), it is possible the diaphram has a hoel that is allowing fuel to run into the crankcase via the impulse passage (crankcase pulses operate the fuel pump).

And remember to completely drain the crankcase when you have the problem corrected and replace with fresh oil.  Hope this helps.