I currently have a 79 15hp Evinrude and a 77 70hp Evinrude. Both motors seem to have the same problem, the float needle valve keeps sticking once I run them, and they won't start after they set a day or two. After going thru the fuel system from tank to fuel pump exit, both motors needed to have the carbs taken off and cleaned. Although I didn't use a new rebuild kit, the motors ran excellent after cleaning..till they sat for a few days, then, the same thing. Could it be the ethenol in the gas??? All the jet holes showed a small, black ring where the rubber end of the needle touched them. Any suggestions would be appreciated..thanks.