Seem all my carburated muscle cars are hard to start after cool down.
Start good when cold but when at running temp and sets for a while, seems to "boil" the fuel out of the bowls ?
Is this what is going on , or am I thinking wrong ?

How hot is the carb getting ? What type ?

Normal 180 temp. 6 bbl holleys, dual carter 4bbl, thermoquads, they all seem to do it. I put insulation under manifold as much as possible, don't know what else to do ?

The insulation under the intake isn’t the plan. It restricts air flow under the intake. These are all B or RB engines ? Id consider reducing exh flow through the intake AND insulating the carb from the intake.

Today's gasoline is formulated for closed injection systems with no regard for evaporation qualities.

Back in the 60s and early 70s, gasoline was formulated to retard evaporation, since almost every car had carburetors open to the atmosphere.

So yes, today's gasoline evaporates much faster than back then.

The plus side is, when the gas evaporates, it does not leave the varnish and other crud that it used to.

The solution is to spray carb cleaner in the intake to allow the engine to start up and pump gas into the bowl. Either that or install an electric fuel pump to be used temporarily during start ups after the bowl goes dry. But don't plumb it so the mechanical pump is trying to pull gas through the electric pump - that won't work.

Actually the problem has existed for many many years.
Todays pump fuels do tend to have higher loss in the lower temperatures of the distilation curve. Howerver the evaporation rates are still regulated both federally and also by many states. Generally RVP is the basis for regulating evaporation, but some places also use 'drivability'.

Any of several reasons for difficult hot restart could relate to fuel and temperatures.
One is the evaporation off of the intake's walls. When the walls are 'dry' on a hot intake then it will take a little longer to get started.
Another is some fuel loss in the bowl but this should be fairly minor. However what is lost, if the bowls got hot, would be the lightest portions of the fuel - then its like trying to build a fire without tinder.
There also may be overfilled bowls. This was a problem with heat on the fuel lines between the pump and the carb.
Finally, any CAP and subsequent emmissions reduction packages ran retarded timing, leaner mixes at idle which had a side effect of increasing hot start difficulties.

1963 Chrysler Master Tech on vapor in the feed line: http://www.imperialclub.org/Repair/Lit/Master/188/Page13.htm
Chrysler Fuel pump bypass kit: https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2288216/tsb-for-fuel-pump-bypass-kit.html

1973 Master Tech "Lets Get Them Started" http://www.imperialclub.org/Repair/Lit/Master/307/index.htm
and the film version: http://www.imperialclub.org/Repair/Lit/Films/307/

Examples of fuel distilation curves: https://www.forabodiesonly.com/mopar/threads/hot-fuel-lines.438352/#post-1972557913
More links about Gasoline: https://www.forabodiesonly.com/mopa...gular-vs-premium.425033/#post-1972367213

Must disagree on that. I have done it that way for many years. Carter mechanical pulls through a Holley electric.

Has the OP blocked the exhaust cross over in the intake?

On the FBBO site, one of the posters found that the current fuel was boiling at 150*. Under hood and running temps are considerably higher.

I'll agree with Dave as I to have done the same. But be aware that the electric must be on when romping on it as it does cause a restriction that will result in a loss of fuel pressure / flow.

FWIW, I've checked my latest Road Runner's AVS for bowl evaporation; after a week of sitting in my shop, the bowls are still half-full.

As for the electric + mech pump flow, ran that setup on my Hemi car and 2 others for 33 years so far, no problem.
One uses the Carter electric, another a Holley 110, a third has a Holley inline.

Yes..... exhaust crossover is blocked

Yep, I run a micro switch on the carb's secondaries to trigger the electric pump along with a manual switch under the dash..........just in case.

Had similar issues with AMC 360 4bbl and cast iron manifold. A phenolic carb spacer fixed the issue. Ordered it off summit.

Has anyone ever tried the Cool Carb stuff? Just wondering if it actually works.

I have run the Cool Carb plate on my 340 for about five years or so. It does cool the carb! I have stopped the car in a parking lot, opened the hood to feel the carb to find it cool and sweating. It was strange. But it does get hot after a normal cool down process. But while driving, it seems to make a difference with the air passing around it.

There is a max temp that CC specifies. Get your tuning correct and you should not have problems. I have had manifolds, iron J heads, aluminum heads, and headers on this engine and each time I pull the carb I make an effort to check the spacer plate. I have not had any problems but others will show pictures of the spacer plates melting.
The owner is a nice guy and I would suggest to ask him what his max temp is and decide from his answer. He has a cool story on how he chose this material. 👍. If I remember correctly, it was used as a heat sinc material where he used to work.