A few years ago my Mastiff wouldn't start. It would turn over and was getting spark and fuel. When I sprayed starting fluid in the carb it would start briefly but wouldn't run. Someone on this forum said it could be bad gas. The bike had been sitting for 3 months. I drained the tanks and carb, put in new fuel, and presto it started and ran fine! After that I started using Star Tron and never had a problem again.