1992 Evinrude 120 erratic rpm at 2500

[Jeff P]

Bought this motor and disconnected VRO and mixing oil in tank. Replaced power pack it had no spark, but good compression. At approximately 2500 rpm I get an erratic rpm but can get through it and runs like a champ. When I throttle back down same thing. Anything over 2700 rpm it runs really smooth and great throttle response. Any idea as to what it could be?

 

[daselbee]

Clogged throttle bodies. Look up my past posts. Read up.

 

[Jeff P]

All 4 carbs were completely taken apart, cleaned and still getting the same problem. Any other ideas?

 

[daselbee]

Throttle bodies. you never say throttle bodies! Carbs are not throttle bodies.

 

[Jeff P]

Now throttle bodies are clean. Port 125 degrees and starboard 150 degrees. This is after 10 minutes running in test tank. One is too cool while the other is too hot.

 

[daselbee]

If it was me, I would take the thermos out (one at a time) and with thermo cover OFF, start engine. Note how much water gushes from the open thermo hole.
Compare that both sides are the same.

Then consider the possibility that the thermo for the cool side might be stuck open. You could also swap thermos to see if the problem follows the thermostat.

You also have a goofy water valving system that aspirates water out of the belly pan. That is on the hot side, so consider that as a possibility.

I assume you have not run it to see if your midrange problem has been resolved.....

 

[daselbee]

Also consider that the 150 degree side is likely the correct temp, considering the thermos are 142 degree units.