2008 Mercury Bigfoot 50hp

by Robin
(Millsboro, DE )

When out on the water, the engine is fine until we speed up pushing the throttle all the way forward. The engine will run fine for about 20-30seconds going full speed, then sputter, keep running, but as if we have the throttle at the slowest speed, even though it is pushed all the way forward. We have had it with a boat mechanic for 8 weeks, he has replaced the Fuel Valve, Fuel Pick up , Thermostat and Thermostat housing, the water pump impeller and battery cables. with no success. Please please help with your ideas.

Thank you
Robin
Rwipf@verizon.net
Sussex County Delaware