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I'm not sure if this topic has been discussed before so here goes.
I was having trouble restarting our '52 Mayfair on hot days. I have an electric fuel pump so I don't think the issue was vapor lock, but rather the gas vaporizing in the carborator. When the air cleaner was removed you could actually observe the gas "boiling" right in the chamber.
I friend auggested adding about a gallon of diesel fuel to every 10 gallons of gas. The theory was that the diesel would lower the volitization point of the gas so it wouldn't "boil".
Does this make any sense to you engineers?
It seems to be working so far. We drove 600 miles on a tour in hot weather and she never failed us once! And it doesn't seem to smoke out of the pipe any more than it ever did!

I would check two things:

First, check your heat riser to make sure it is working correctly and not stuck.

Second, do you have the insulation spacer between the manifold and the carb base in place?

The diesel should do your engine good. Not only will it cure the hot hard starting, your engine should run better and cooler on it and possibly even start easier when cold.

Your engine has rather low compression and low octane fuel suits it best. Diesel lowers the octane of the gas.

The long stroke, slow revving design also takes advantage of the slower burning heavy ends.

Of course there is a limit to how much diesel you can burn but it sounds like 10% is working fine.

If there is any smoke you could try kerosene instead of diesel. It is lighter and should burn better.

Have you noticed any difference in power, coolness, smoothness or anything?

Denny, BigKev made two excellent suggestions, and let me add a third. Many models used fibre insulators around the fuel pump-to-block bolts, and a heat shield around the fuel pump. Some other models also used an insulator block between the fuel pump and the block. The purpose of these were to prevent heat from the engine block from heating the fuel pump and such heat can then be transferred by the metal fuel lines to the carburetor and indeed the entire fuel system. Rubber links in the line to the tank, for example for an inline filter or electric pump, can exaggerate the problem by eliminating the gas tank and its contents as a heat sink. I suggest you check the parts book to see if these items were used for your particular model, and if so check and make sure they are present.

BigKev, the heat riser was checked out and its ok, but not sure about the heat shields.
Rusty, I think that kerosene would probably burn cleaner too but when you're out and about, sometimes it's hard to find. As far as running cooler...not sure, as it always runs pretty cool even in hot weather. I have plenty of power and it indeed runs smooth.
Owen, are you saying that the rubber gas lines should be eliminated?
Thanks to all...

Do you have the 1/2-3/4" thick insulator block between the intake manifold and carb base? If the fuel is boiling off in the carb, then I bet the carb is getting way to hot.

Didn't some of the 51-52 senior cars have an additional carb heat shield when the 4-bls first came out?

Oops, foot stuck in mouth again! I did ignore that we have to have one rubber link, the hose between the fuel pump and the line to the tank so I suppose more of the same back by the tank doesn't make a difference - sorry about that oversight. But the point remains that anything in the fuel system that inhibits transfer of heat from hotter bodies to cooler bodies is certainly not desired. And visa versa.

If insulators between fuel pumps and the block, between the carburetor and mainfold, between fuel pump bolts and the pump body, and heat shields were all considered essential with the "good old gas", they are even more necessary today. And though I have no firm evidence, I can't think that a rubber section between the fuel pump and the carburetor is a good idea.

Can I assume that mixing a bit of diesel with into fuel for Packard V-8's would not pose any problems?

I'd think it depends quite a bit on which V8; many of the 374 engines barely avoid excessive preignition on 93 octane gasoline.

Cutting the octane on a V8 would be a bad idea. They are high compression engines and need high octane gas.

The octane of the gas should look like the compression ratio. In other words if you have 8.7:1 compression use 87 octane regular. If you have 9.3:1 compression use 93 octane hi test.

If you have 7:1 compression you can use 70 octane, except they don't sell such gas anymore so you can cut your regular with a little diesel, kerosene or stove oil.

Naturally this is not an exact rule, just a guidline. But if you have a 10:1 compression motor you will probably need octane booster or water injection while if you have a real oldie from the 20s with 4.5:1 compression you could use up to 25% kerosene.