My Murray push mower has a 550 series Brigs and Stratton engine. Very difficult to start, and when stopping it won't start or will erratically run. The air filter saturates with gas and oil. Squeezing out the filter will allow it to start but run erratically. We cannot mow the lawn at all. Need to know how to restore normal operation. The mower is about 1 yr old and until recently operated dependably.