Old gas
 

I have old gas in my boat. I have modified 502EFI's that have run great for many years. Due to various circumstances we've not boated any for two years. I have the boat for sale and did a demo run with a potential buyer. The motors sputtered and ran horribly and didn't want to idle in gear. The marina shop is in the process of getting the old fuel out and I plan to put 40 gallons of no ethanol 93 octane back in. Is it reasonable for me to assume that the new fuel, when it gets into the system, will return most if not all of my engine function and performance ? Any other suggestions for this procedure ?

Thanks in advance for the help,

No need to put 93 in it, wont perform any better 87-89 is what the engine is built for, it may be ok if the fuel system and injectors are not fouled up