I recently had the same experience with a 1959 Dodge D100. I got it started on the 15+ year old gas. It ran but it was a little lean. I cleaned the carb and it ran better but still lean. I think that the gas had lost most of its volatility. It since ran out of gas and I havent had time to pour fresh stuff in and try again. I do know that todays fuels go varnishy in a few months. I was amazed at the old gas.