late 80's 40 HP Evinrude surges at full throttle

[mkjconsulting47]

Motor starts well and runs fine until after 75% thottle, then it surges back and forth a bit at all throttle settings up to full open. Last year it bogged down at 1/2 throttle at end of season and I discarded the gas and put all new gas in this year plus new spark plugs. any ideas? I am a novice outboard motor person. The motor is on a 16 ft aluminum fishing boat and moves it very well.

 

[CharlieB]

Re: late 80's 40 HP Evinrude surges at full throttle

Most probably a weak fuel pump. Prove it before spending money, test run once more and when it begins to bog start pumping the primer bulb on the fuel line, if it is a weak fuel pump the engine should respond.

 

[JT!]

Re: late 80's 40 HP Evinrude surges at full throttle

check your tank's air vent, also check for obstructed gasline.

if you squeeze the bulb, does it quickly regain its shape or is it very slow?

 

[rpena]

Re: late 80's 40 HP Evinrude surges at full throttle

check your tank's air vent, also check for obstructed gasline.

if you squeeze the bulb, does it quickly regain its shape or is it very slow?

So I know this an old subject, but what was the problem? I am having the same problem. Mine is a 1983 25hp Evinrude on a 14' aluminum Rhyan-Craft. At full throttle flying across the lake then after 3 to 5 minutes it starts surging....?Like it's running out of fuel....?