OK, I need help, I have a Murray Select model 425600x8a with a Briggs&Stratton engine OHV 18.0 I/C. My first challenge was it did not wanted to start, I notice there was some gas mix with the oil so I change the oil, oil filter, spark plug, gas, gas cap (it was not closing all the way). After doing all of these changes still the mower starts but for just about 3 to 5 seconds. Any suggestion?