Smoothing out a 1990 Evinrude 30hp (Ignition and new prop)

[biglurr54]

I am trying to smooth out my 1990 Evinrude 30hp motor. I have it on a 16ft pontoon. I do not have a tach hooked up to it but I can hook one up to get some readings. I would like to get a 4 blade pontoon prop.

The engine stumbles and shakes at varies rpms. I have to adjust the throttle slightly to smooth the motor out. It seems to miss a lot. I am planning on doing wires and plugs on it. I did them 4 years ago. Is there anything else I should inspect and do in order to try to smooth out the motor?

What would be a good prop for the motor? (i know tough to call but I have no idea where to start), I would prefer to under size the prop so it relieves the pressure on the engine and i can back off the throttle to prevent over reving. I did that with my 120 and was very happy with it.

 

[racerone]

I think that new wires every 4 years is not needed !------What trouble shooting have you done if any ?----How about a compression test.----Have you installed a new water pump impeller recently ?-----Checked the flywheel key ?

 

[biglurr54]

I think that new wires every 4 years is not needed !------What trouble shooting have you done if any ?----How about a compression test.----Have you installed a new water pump impeller recently ?-----Checked the flywheel key ?

I did a new water pump and lower unit seals last spring. Other than that, i haven't diagnosed anything as the stumbling isnt terrible and i know with my 120, first thing to do is plugs! It starts and runs but has a stumble at certain rpms including at idle. a slight advancement in the throttle clears it out. The carb has never been touched.

 

[boobie]

Do a cylinder drop test on it. Maybe that will tell you something.