I have a five- season- old riding mower with Briggs@Stratton motor model 31 H 777,type 0605 E 2, code 050805ZD. It has been well taken care of and gas stabilizer added as required. Last September, as the season was winding down,it would start and run as usual but only for ten minutes or so, cough a couple of times and die. After letting it set,it would do the same but the run time varied,sometimes the running would last for half a mowing and I was able to worry along to the end of mowing season. I drained the gas tank and installed new fuel filter which helped not a bit. Could ethanol in the gas be the trouble? Any and all suggestions I would appreciate. Billyjo