Seems pretty quick for fuel to go bad, my 78 D300 only gets a taste of fresh fuel 3-4 times a year, no problems BUT, it's a stock low compression 400, don't take much to get spark.

I've been using ethanol free in small engines that are finicky (honda generator) or old (87 yamaha warrior) that has no tolerance for ethanol.
It's worked so far, both start and run like they should.

Ed