I have a Honda hi-wheel self propelled mower. This spring I had it serviced by a reputable dealer and it has been working fine all summer, until today. The mower will start and run for about 10-15 seconds, then it stops. I checked the oil, air filter, spark plug etc. and all were fine. I have fresh gas with the additive to prevent the ethanol from gunking up the motor. I also have a Troy-bilt roto tiller that is doing the same thing. Does anyone have a suggestion on what I should check next?