Rec 90 is low octane fuel ethanol or no ethanol its still low octane fuel and a real bad idea for a supercharged motor.
Any fuel will go stale if it sits long enough. Ethanol add or not. Don;t matter. Its just old stale fuel that won;t run good any more. Just drain the old fuel and fill up with the best pump gas 92++ octane and add the race gas as you like to your liking to boost the fuel octane. I recomend you add unleaded race gas 110 or higher rated.
Your carb may have injested some varnish from the old stale fuel. Your spark plugs may now be fouled and need replace ment. clean out the carbs and replace the fuel filter and replace the old fuel.
Again running 90 octane gas in your supercharged engine is not a good idea. Ethanol or not.