6. What could cause a smell of gasoline in the crankcase? I noticed a slight smell of gasoline the last time I checked my oil.

The smell of gasoline in oil is almost certainly caused by a small leak in the diaphragm of the mechanical fuel pump. This condition can be quite serious. In worst cases, fumes can collect to the point that they can ignite within the crankcase. Historically, the worst damage we have ever had reported (in this case, a second-hand report) was a flywheel cover being blown from the front of the engine (although the engine itself kept right on running!).

What happens is that a small pinhole develops within the diaphragm, which allows fuel to pass into the bottom of the pump housing and into the crankcase through a small oiling hole in the block. The danger is that the pump can still usually keep up with the demands of supplying fuel to the carburetor, which means that these small leaks might go undetected for rather long periods of time.

Other indications of leaky diaphragms include blackening and/or thinning of the oil, and eventually a rising of the oil level within the crankcase. - Updated: November 9, 2003