[STB]

At about 200 hours my 610 Mule's fuel pump began pushing oil into the carb and gas into the crank case. This caused the engine to stall and the oil to thin and smell of gas. I replaced the fuel pump, gas filter, and breather between the fuel pump and crank case as well as the oil and oil filter. Now at 268 hours my new fuel pump is doing this again. What is causing the fuel pump to again go bad??

 

[99prairie400]

Excessive crankcase blow by that is not being taken away by the recirculation system could overextend the diaphragm and tear it. The fuel pump works off of the differential pressure between the crankcase and atmosphere when the piston goes from TDC to BDC. While that pressure goes away the moment the piston starts back up the bore (then becoming relative vacuum) there is a separate mechanism that caries away blowby to the intake manifold do have the gasses reburnt. If the second system is clogged somehow (either the hose going to the manifold is kinked or the rubber has turned and peeled off the inside and is clogged up) the fuel pump is being pressurized to one side beyond the normal extension and would quickly put a hole in it.