engine dies at high throttle

S

soldier side

Cadet
Joined
Mar 20, 2011
Messages
25
Hi, Just took new boat out for the first time today, and am having some problems.
engine is 1988 merc 40 outboard.
starts up great, and good smooth idle, i can get up to about 1/3 trottle, and it cruises ok, probly 15mph (spedo is broke, just guessing), but while cruising, the engine will change rpm randomly and ill get a spall burst of speed for just a second, then rpm will drop again. if i go above 1/3 throttle, engine will sputter and die. If i hold the engine at half choke, i can run full open no sputter, no rpm changes, but only 20-25mph. engine is on a 1977 thundercraft titan 150 15' bowrider.

thanks for any advice.
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: engine dies at high throttle

Anytime a motor will run better with the addition of the choke, it is time to clean the carb.

While you have the carb off for cleaning, test the fuel pump by cranking the motor for a few seconds while watching for a strong pulsed fuel flow. If flow is weak then rebuild the fuel pump.
 
S

soldier side

Cadet
Joined
Mar 20, 2011
Messages
25
Re: engine dies at high throttle

Thanks, will try that in the next few day, whenever the rain stops again :(
 
S

soldier side

Cadet
Joined
Mar 20, 2011
Messages
25
Re: engine dies at high throttle

finally got a break from the rain, and freak snow storm, and got the plugs changed and ran soem seafoam through it, and a ton of carb/choke cleaner, and sputtering has stopped and can run wide open w/ no choke, but for some reason still can't get the boat to plane out, prop has some dings and dents, possible cause, may too small of an engine?
 
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