81 Evinrude E150TRLCIA

[Dbrown4827]

Motor runs great for a few minutes; at full throttle the boats planes quickly with plenty of power. After a few minutes it then acts like it's starved of fuel and under a heavy load but does not die. Pumping the primer bulb will help keep the motor running at full power.
What I've replaced: new plugs, new vented gas caps, new fuel lines and primer bulbs, fresh fuel and oil mixed at correct ratio.
I'm thinking it's a fuel pump but not sure which one to replace or if I should replace both. Any suggestions are greatly appreciated.

 

[oldboat1]

what ratio are you using?

 

[Dbrown4827]

50:1. I've been careful to mix 2.6oz to each 1 gallon of gas. Pre mixing 5 gallons at a time to make sure.

 

[oldboat1]

sounds good. That reference to two cap vents -- running a single tank, maybe dual tanks with a switch? If an internal tank, always a possibility of water contamination.

 

[Dbrown4827]

The previous owner stopped using the built in tank (not sure why) and I have 2 6 gallon plastic tanks that I use a switch. I replaced both caps just in case they weren't venting properly.

 

[racerone]

Just install a new diaphragm in each pump.-----About the only thing that can go wrong.----Pumps are driven by crankcase pressure pulses.-----There may be issues there.----Post the CYLINDER compression test results here.-----That may offer a clue.