I've been chasing gremlins for a while now.  Per my earlier post, I think its mostly carb issues.  I've had it apart cleaned it put it back together a few times, including new components from a kit that you can reach by removing bowls.  i've had mixed results.  Sometimes runs rough all the time, sometimes runs good but surges at idle, sometime runs good every way but then doesnt.  Anyway, carb is a work in progress.  I'll get it. 

But while doing general trouble shooting, a friend who is pretty good at these things said my dirty greasy plug wires could be arching.  I cleaned those up. (havent run at night to look for arcing)  May get new wires.  With all my carb fiddling, it had been running real rich, so all my plugs were crispy black. Put new ones in. 

Now my question.  He suggested a general electrical survey. 12+ volts at battery.  12+ volts at solenoid.  But 10.4 volts at coil.  (electronic prestolite, so no ballast resistor.)  So it appears somewhere between solenoid and coil (like around the key?) I've got a voltage drop.  If its been there all along, but has run fine with it.  If voltage drop is new, maybe contributing to problems?  I really dont feel like tearing dash pod out, but is that 10.4 V at coil worth tracking down?

One other question, back to carb.  Current situation, runs pretty good at higher rpm.  Serious surge at idle.  Putting mixture screws all th way in does not kill engine.  I've cleaned carb body and metering block passages a million times, so I dont think its dirty passages anywhere.  Any other ideas?

 want to eliminate your headaches, replace the engine harness. they are still available for SBF, and small block chevy carb engines. basic marine wire harness with all new ends. tinned wire and rubber covers. these harnesses on some of these pcm engines are 50 years old or better. one of the reasons i hesitate to work on older boats is because of how i usually find the wire harnesses in them, worn, been in the bilge,bent dry rotted and poor conductivity. and as usual lots of side cutters and automotive or household connectors in the mix.

When you're checking that voltage with the key ON and engine OFF, along with what TRB mentioned you're also powering the electric choke and alternator excitation, both of which will cause reduced voltage to the coil whether you have good wiring or bad wiring.

If you're concerned, make a small jumper with alligator clips on both ends and run it from the solenoid to the coil positive and see if the engine runs any differently.

Speaking of coils, maybe you have a bad coil......you've been through that on the old boat. Coils can cause all kinds of "erratic" behavior like you seem to be having.

It's always a good thing to have a spare coil around for "troubleshooting" purposes 

On your 1997 ish carburetor, you have that little accelerator pump transfer tube between the primary metering block and the carb body. Does that have 2 good O rings on it ? Bad O rings make for an unmetered flow path that makes things rich running (bypasses the idle circuitry so shutting the mixture screws has little or no effect)

Here's a picture with one O ring showing and the other one on the end pushed into the metering block.

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New power valve ?  A power valve with a leaky, cracked, ripped diaphragm or the wrong gasket gives an unmetered flow path for fuel that'll make things rich running ( same as above, little or no effect when shutting the idle mixture screws)

KENO wrote: Assuming that the 10.4 volts is with the key ON and engine OFF (based on your 12+ numbers at the battery and solenoid) it's gonna be higher with the engine running and the alternator putting out 14 or so volts. When you're checking that voltage with the key ON and engine OFF, along with what TRB mentioned you're also powering the electric choke and alternator excitation, both of which will cause reduced voltage to the coil whether you have good wiring or bad wiring. If you're concerned, make a small jumper with alligator clips on both ends and run it from the solenoid to the coil positive and see if the engine runs any differently.

Tested voltage with engine off, so good point about draw on that circuit.  Dont think we checked with engine running.  Did do the jumper thing.  Did not make a difference, so maybe not an issue.

KENO wrote: Speaking of coils, maybe you have a bad coil......you've been through that on the old boat. Coils can cause all kinds of "erratic" behavior like you seem to be having.  It's always a good thing to have a spare coil around for "troubleshooting" purposes

Not at coil yet.  Started the throwing parts thing.  Have purchased (waiting for arrival) cap and rotor.  Contact on rotor looked pretty worn down.

KENO wrote: On your 1997 ish carburetor, you have that little accelerator pump transfer tube between the primary metering block and the carb body. Does that have 2 good O rings on it ? Bad O rings make for an unmetered flow path that makes things rich running (bypasses the idle circuitry so shutting the mixture screws has little or no effect)

Hmmm.  Interesting.  Explains one symptom - the mixture screw thing.  Not sure about O-ring.  Boat is put away for several days, I dont feel like pulling carb apart for the umpteenth time right now, but I will check it.

KENO wrote: New power valve ?  A power valve with a leaky, cracked, ripped diaphragm or the wrong gasket gives an unmetered flow path for fuel that'll make things rich running ( same as above, little or no effect when shutting the idle mixture screws)

Think power valve is OK.  Guy helping meNext ste had same thought.  Tested it by laying it down and adding some fuel to the top side.  Waited a while and saw no fuel leaking through.

Next steps: Run with new cap and rotor.  Disassemble carb (again) check o-rings on AP transfer, check PW gasket. I'll let you know.