engine miss at mid rpm

[chenta]

I have a 1987 evinrude 110hp that has a jet pump that I have a miss at mid rpm. Runs fine at lower rpm below 1000 and 3500 to wot 5300. At 2500 it starts to miss alittle but if I trim the engine up it goes away. Could this just be a simple float adjustment

 

[the machinist]

Re: engine miss at mid rpm

Since your motor is functioning with a jet unit & trimming it helps, are you cavitating? Sucking air? However this will usually allow the engine to wind up with no movement of boat.

You might consider putting side skirts on the suction intake.

 

[chenta]

Re: engine miss at mid rpm

If I trim it up to far then yes it will over rev, but i am aware of slippage on props and jetpumps and the damage that it can do so I don't let that happen. In looking at the pump intake foot there are holes where someone at sometime had some type of skirt but the engine miss happens when the pump system is in the vertical position so I don't believe that it is a cavatation problem. I can feel the boat surging as the miss comes and goes