Ive been having this same propblem... to an extent. I have a 90 Four Winns with a 5.7 atnd the factory quadrajet carb, was getting alot of hesitation on accel and top end wasnt the best so new plugs, wires, cap, rotor, new fuel line that was gummed up and was better but still room for improvement. then about two lake trips later the bottom fell out and she wouldnt hardly idle, kept loading up and WOT was about 3800 and was very hesitant... carb kit and BOOM! ran like a top... for one day... then back to it running like crap with only 38-3900 rpm. The last couple tanks I have been running 87 ethanol ($150 fill ups that last 1 day were getting old!) and 1 tank i dumped 3 cans of seafoam in the 87 ethanol. boat calls for 89 No Ethanol so Im going to burn all the rest of this off in the next day or two and try the 89 or 91 No Eth... Im at a loss now unless theres a bunch of junk in the tank coming up, fuel filter is next again
