Yamaha 4.3l stern drive idles but no power above 2100rpm

[MerryO]

This is my third summer with this boat. I know about all the difficulties finding the special Yamaha parts, but I've been able to winterize and keep running smooth with aftermarket parts. Earlier this summer, she would run rough for a while, then after a period of high idle, she would seem to warm up and run fine.

Now, she idles fine, and I can get higher RPMs in neutral, but she bogs down at 2100 RPM when in gear. I've changed the plugs, new plug wires, new rotor & distributor. No improvement.

I'm thinking fuel supply and/or carb issues, but wanted other opinions. Going to do comp tests on all cylinders before pulling the carb for rebuild.

 

[Bondo]

I'm thinking fuel supply and/or carb issues, but wanted other opinions.

Ayuh,..... Welcome Aboard,.... I concur, inspect the Contents of the fuel filter for anything but gasoline,....

 

[Glass_On]

Same symptoms as my brother in law's boat. After checking the oil, there was about 3 quarts over. Turns out the mechanic's son added the oil thinking it was empty.
Don

 

[MerryO]

Recently changed the oil and filter (beginning of season). Oil level is correct.