1982 75hp Evinrude not reaching max RPM/speed at WOT

[lazeronu]

Good morning,

Long story short. Took boat out first few times, Ran at 5200 rpm and 34mph WOT. Next time i Was out on the water and was WOT and i noticed RPM dropping. They gradually dropped to 4200 rpm and 22mph and held there. Was never able to get it to reach max RPM again while under load. Idling, no problem it would reach max RPM.

I have checked compression on all 3 cylinders 130-140psi. Spark on all 3 plugs. Pulled plugs while WOT and all 3 would notice a drop in RPM.

Sprayed carbs with Carb Cleaner. All 3 butterflies run horizontal at WOT. Ran Seafoam through the fuel.

Prop is 12.5x 19.

Any help would be much appreciated. Trying to troubleshoot before bringing it in to a shop.

 

[emdsapmgr]

Could be a weak fuel pump. When the engine starts to bog/slow, have a buddy go back to the fuel hose bulb. Squeeze it constantly. If the engine picks up and runs WOT as long as you keep priming the fuel hose bulb, you have a fuel delivery problem. Which could be a weak pump. Weak ignition components tend to fail once the engine heats up to normal operating temps. This could be happening to your engine. It may be dropping spark to one plug after the engine runs for a while. Once the engine cools, of the plug may fire again till the engine warms up. Your compression is good. I think you may find that 49 cubic inch block may perform better with a 17 pitch prop. That 19 is pretty tall pitch.