1989 Evinrude 90 HP Boggs down at full throtle!

Issue:

Motor idles well, when accelerating to full speed, motor (after say 2 mins) starts bogging down, and throltle lever has not effect on acceleration etc, then if I back down on throtle and wait say 2 mins, full power returns, and the above repeats again, if I self prime at the ball it work again for 2mins.

Also if i run at low speed the motor start to bogg down, the hand prime is need to keep motor running as fuel starts to run out.
Prime ball was losing prime(not staying Hard), So I changed the ball with a new ball, thinking this would fix the issue. did not work(Yes It is the correct ball, rated for this motor, etc etc etc.

Had a Machanic clean the carbs, still doesnt work.

New Plugs, new fuel seperator, new pug wires,etc..

Anyone had this same issue??

(Supplemental info: 50:1 fuel is used)

Thanks in advance for your time and consideration.

Check the flapper on the fuel piston in the pump.---------------Repair kits are available for these VRO pumps.

racerone said:

Check the flapper on the fuel piston in the pump.---------------Repair kits are available for these VRO pumps.

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A similar thing was happening to my 120Hp, and I had to change the water pump assembly as the impeller was worn out. Do you get all the warning horns, like on startup or when running low on oil? This could also be a thermostat problem but check the water pump impeller first.