Mid RPM Miss need Help

I am having problems with my 1978 Cuddy with an OMC 350. It runs great except from about 3000 to 3400 RPM then it has a slight miss. When I open it up it goes away or if I keep it below 3000 it is gone.
It runs about 4200 WOT at 36 MPH.

I use the boat on Lake Erie and very rarely run over 2800 RPM. I noticed the miss towards the end of last season. This season I made the following changes:

-     Removed gas tank and cleaned it out, lots of gunk from years of neglect
-     Installed new fuel lines from tank to fuel pump
-     Installed new fuel filter
-     Installed new Pertronics Electronic ignition
-     Installed new coil

The cap, rotor and wires where new when I bought the boat 2 years ago.

When I installed the electronic ignition, I started the motor up in the driveway and set the timing to 10 deg. I had to move the distributor quit a bit as it was too far advanced. When I moved the distributor back to 10 deg. I had to adjust the idle screw up slightly.

What should I be looking at next?

since you had a lot of gunk in the tank check the vent/check ball at the tank and make sure it's clean as well. Also check and make sure a wire isn't loose at the cap or at one of the plugs.

Why did I have to increase my idle stop after adjusting the timing after I installed the electronic ignition module? I would have thought that it would be the same with points or electronic? It is a chevy 350, I set the timing to 10 deg. is this correct or should I be more advanced?

2_Nautiques wrote: Why did I have to increase my idle stop after adjusting the timing after I installed the electronic ignition module? I would have thought that it would be the same with points or electronic? It is a chevy 350, I set the timing to 10 deg. is this correct or should I be more advanced?

I would think that the reason you had to increase idle after installing the Pertronix is that your timing was advanced a little too far when you had your points in. Advancing timing at idle (to a certain point) will increase idle speed. 10 degrees at idle sounds pretty close for your engine. It's best though to check timing advance at 3000 RPM with a variable strobe light. The SBC likes about 34-36 at 3000 RPM.