50hp Mercury acting up

[benningtonr]

June 6, 2016 at 1:43 pm#1623199
I have a 50 horse Mercury. Starts and sounds great. Put it in the water, max RPM is about 3400. Should be pulling 5500 easy. Boat has the original prop, it is in great shape. Talked to a local shop, the suggested quick Kleen fuel treatment and 2 stroke oil. Due to fuel pump might be a little dry from sitting for 6 months. It has ethanol stabil in the fuel. That bumped it up to 3800-4000. Still not getting the 5500 i think i should.
Run her on the water for a couple hours and now if i keep it abouve 2200 after 5-10 min it will act like it is dying, but it never dies. i back the throttle down it idles like a kitten, i pour the coals to her and 5-10 min it does it again. but with each time the run time is less, last time i had to keep the rpm?s at 2000 or less, or it would start acting like it wanted to die. If I left the throttle in position, it would buck, cough and the rpm?s would come back up, then buck cough sputter, but never die, then the rpms would rise back up.
All of this second one happened the same day.

 

[racerone]

Do the following.---Do a compression test.-----Then check and make sure you have good spark on each lead.----Good spark is spark that will jump a gap of 3/8" or more.-----Has exhaust been checked for blockage ?----Has water pump impeller been changed ?----You must verify that both carburetors are clean and that the diaphragms on carburetors are good.---A fuel blockage can destroy a fine motor !!----And have you test run with a " known to be good " tank and hose ?

 

[benningtonr]

It is going into the shop, I was hoping it might be something simple. I work on switches/routers/firewalls, not cars/boats

 

[CamaroMan]

i had the same - unless its something else your stator high rpm (red wire?) might be going.. or maybe throttle cable issue / carb linkage issue / fuel delivery / etc etc