My 1986 AQ271C (rebuilt with Summit alu heads, Edelbrock carb and HEI distributor) starts fine and idles fine when cold. After a long trip, it's hard to start and even harder to idle. But after 5-10 min of rest, it starts like a charm again.
What could this indicate?

Now and then, I read a failed alternator regulator can cause trouble. Mine broke some time ago, so I removed it, but battery is very strong and can almost run a full season without charging. I would understand a partially failed or ground shorted regulator could cause problems, but not when it's removed out of the circuit?

 

could be a fuel pump or fuel pump relay issue. Do you have a mechanical or electric pump? does your carb have an automatic or electric choke? does it look to be in the correct position when warm? what's the system voltage when running? Keep in mind, a charged battery produces about 12.6V and the alternator puts out something in the 14V range so its possible that running off the battery vs an alternator can mess with some components.

 

It has a mechanical pump, and it's quite new. Choke is disabled/removed. I don't know the system voltage (have a 80s gauge that is really bad, I'll upgrade the entire instrument panel during the winter). Most of the wiring harness too.

 

well, the idea of the choke is to enrich the mixture when the engine is first started then its turned off and the carb jetting and mixture screws control the warm engine mixture. Sounds like your carb may need a rebuild or tuning adjustments and you may want to confirm the proper sized jets are in place. How do the plugs look - gray/ash color or black/oily? The other possible run issue is ignition or spark, but in that case I'd think you'd have issues regardless of engine temp. PS you don't need a instrument panel gauge to test the electrical system. A $20 volt meter (aka VOM) from Harbor Freight will do just fine. With the engine off, measure across the battery terminal. Now with the engine running, measure again across the battery terminals. Have you recently done a basic tune up - new plugs, wires, cap etc? with your new VOM, you can also measure coil resistance to see if that's up to spec as well.

Note that with a carb, there's no real concern about fuel pressure. All the pump does is keep the carb bowl full which doesn't demand much pressure - something on the order of 5 PSI where a FI carwill be in the 40-55 PSI range to generate the squirt (thus the need for an electric pump).

 

The carb is a "brand new" Edelbrock (3-4 years), and was just adjusted by a drag race mechanic. He's not so familiar with marine engines, but 40+ years experience with V8s. It's the same guy that rebuilt the whole engine 3-4 years ago (with new edelbrock carb, summit alu heads, bearings, etc). Earlier this summer, it was running rough and I discovered the coil was failing so I upgraded to a "china" HEI distributor (with internal coil). Also new Summit DIY coil wires.
The boat is up for storage now, and I didn't check the plugs. Will it still have the residue if I check the plugs?
How do I know the proper jets for this 350 GM?