High octane fuel burns more slowly than regular- - - -sort of like running slow-burning smokeless powder in a "magnum" rifle with a long barrel. It's not really needed or useful in a low compression engine like a stovebolt. You're likely to see much higher temperatures in your exhaust system, as some of that high priced gas does some of its burning between the engine and the muffler, and the exhaust valves won't like it.

Try doing a pressure/volume/vacuum test on the fuel pump- - - - -I suspect that the inlet and outlet check valves in the pump have gone south. There are several places that are highly recommended by members here that will rebuild your pump with ethanol-friendly parts. Good luck!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!