Hard starting conundrum

[rhstewart]

I’m curious what people think about my engine starting problem.

I have a 1967 C20 I’ve been making run since summer 2022 when we picked it up from grandma’s driveway. Grandpa bought it new. The engine was replaced at some point. It’s a 350 block with a 283 intake manifold and ram horn exhaust manifolds. It has an HEI ignition system.

I’ve completely rewired the entire truck with AAW classic update. I replaced the rotor and cap. All the spark plugs were new a year ago. The spark plug wires are new. I recently checked the compression and that seemed fine (all good, one a bit low).

I replaced the carburetor with a new Holley 2 barrel. It seems to work fine. I’ve tuned it according to the manual. The vacuum advance is hooked up to the ported vacuum, which is what the manual says.

I’ve played with the timing. It’s now set at 8 degrees BTDC at idle with an idle around 600 rpm. I’ve had it at a faster idle but adjusted it back to the 1970 350 setting in the Haynes manual.

It starts pretty good with the manual choke all the way out then pushing it in slowly while I let it warm up patiently. It’ll get running and then drive fine. I haven’t driven old cars in a loooong time so my expectations may be off. Maybe it’s fine, maybe it should be better.

If I stop it for a short amount of time it starts up just fine.

My issue is this: if the engine stops while warming up or I try to start it after it’s cooled a bit it takes a lot of turning over to start up again. Pumping the accelerator sometimes helps. Holding the accelerator down sometimes helps. Pulling out the choke part or all the way sometimes helps. I can’t pin down what works but it eventually starts up.

What, exactly, is going on when a truck is cold and hard to start. Cold, thick oil, I assume. Anything else?

Why does choking the carburetor help? I know it increases the fuel ratio but why, exactly, does that matter?

Any other thoughts on my root issue?

I’ve considered replacing the distributor body. Possibly the vacuum or mechanical advance are not great? I know the mechanical advance does something, I can see that. I haven’t tested the vacuum advance.

I apologize for the length. Every time I typed something I thought of something that could be asked.

Thanks in advance!