40 HP sputters @ WOT Runs fine otherwise

fastback66

Cadet
Joined
Jul 5, 2011
Messages
7
Just bought a boat with a 1983 40 HP Merc 2 cylinder Outboard. The motor starts fine and idles good, runs well into mid throttle then sputters as I try to go full throttle. I am thinking it may have bad fuel? Had a half of tank when bought topped off with fresh fuel. I replaced the external fuel lines and primer bulb. Could it be a weak fuel pump? Any help is fine!!
 
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