My 318 has run great , a little hard starting but it will start. I must confess I thought the hard starting was due to a weak fuel pump on start up only. I heard of a small trick to mount a squeeze bulb ( like used on an out board) in the gas line. This really helped the issue on start up for the last couple of years. Now a new issue has started . The 318 starts and runs for a while 2- 5 minutes and will just kill , not starve for gas before dyeing, but just kill. Then it will not start until sitting for a while . The only thing that was done differently in the operation of the unit, is last time while blowing snow, I switched the gas valve, the one that has the reserve setting , to reserve . I have never done this before on this tractor. I did it because I knew I was getting down there on gas and wanted to finish the job with no issue , which I did . Since I refilled the tank with good fresh gas and reset the valve to the normal run positions the issue started. Any ideas what could be causing this problem? I believe this 318 has the electronic ignition. , Thank You.