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??