Bill,
Question... (first a bit of a story....)
Last year on our annual trip downriver we experienced what might be the same issue that you have run into. However, the problem was on the return leg of our trip and the Port engine had been running for over 4 hours. We were running about 1750 RPM on our Chrysler 318's. Suddenly (without any warning) the Port engine "hiccuped" <dropped RPM's down to about 850> and then recovered. It ran fine for a few minutes then "hiccuped" again, also dropping to about 850RPM and then recovered. Finally, on the 3rd event, the RPM's just dropped and the engine quit. It would start but immediately dropped RPM's and died. We made the final 3 hours from Aurora, In. to our marina (Manhattan Harbour) on 1 engine. When we arrived, the port engine did start and we were able to dock normally.
This year, thinking that the problem was a fuel pump (manual type - we'd had a similar issue with the starboard engine and I replaced that.), I replaced that (pump). We made only a few short trips this summer (about an hour each) with no issues. On our annual (non) trip this year, we got 50 minutes out of the marina when the port engine did the exact same "hiccup - run - hiccup - run - die off" sequence. We came back to the marina on the starboard engine. Trip canceled.
So I'm stuck with what appears to be a ton of options. Your distributor cap / rotor replacement adds to that....
I had replaced both engine caps and rotors (along with wires) 2 seasons ago which I got from NAPA (brand - unsure).
What's been suggested / considered:
1. Fuel issue - new fuel water separators this spring (need to pull port and see what the contents are), inline metal cannister fuel filter this year, Perko filter (need to check), screen filter at carburetor.
2. Fouled gas - need to pump from bottom of tank and see what it looks like.
3. Possible coil breakdown when heated up.
4. Your fix with replacement of the distributor cap and rotor.
There also seemed to be someone that had a similar issue that detailed his issue/fix on the old site but I can't seem to locate that.
Any thoughts? Anyone? (isn't a fix by acclimation
but if I haven't thought of it, better to have someone else who may have a possible cause/fix.
Bill