When you experience warm weather vapor lock, you can actually see fuel bubbles passing through the sediment filter assembly fuel bowl. What effect, if any, have you had with switching to ethanol free fuel or closing the heat passage valves on your intake manifold? Have you tried any additives to change the RVP?

 

Interesting. I have not had that problem even here in blazing hot Florida. Curious as to what folks re doing should that occur.

 

We have experienced it on 2 different Tri-carbs. Neither uses headers. Both have the intake heat passages open.

 

It's a old problem made substantially worse for low fuel pressure carbureted engines today, especially now after fuel reformulation. Pump gasoline for years now is formulated for fuel injected engines with something like 40psi or higher rack pressure and electric fuel pumps pushing from the tank position forward. All of the fuel line clothespins and heat wrap cloths and the many things guys try wont change the fuel properties to make hot weather starting and running easier. The bottom line is in my opinion and experience nothing short of a electric booster pump pushing from the rear will make hot starting easier.

Older cars with carburetors also vapor lock while driving up the road on hot days. 50's, 60's 70's cars, even A model Fords with gravity feed fuel delivery. I can't say if the use of off-road gas alone is a workable expedient to this on going trouble as I haven't tried it. I can say positively blending 100LL av gas with the cheapest pump gas I can find is a certain solution and one I would use anywy for high compression engines. Yes, high cost of off-road fuel is also ±$6 gallon here. Racing gas does a good job too but its likewise extremely expensive.

This all assumes of course your fuel delivery system is in good shape all up to snuff. Enigne not running excessively hot on hot days.

One last suggestion is I have settled on Shell V-power gasoline as it seems to do the best job for me in hot weather of the common brands around here. It will still start hard on hot days which has failed 6V starters running on 12V in my 1952 Olds cars. They have 1953 303 12V starters now which solved that headache. As you observed with your glass fuel bowl, you can actually hear the gas boiling in the carburetor witrh the engine stopped, until that fuel is gone making either a electric pump boost or much cranking necessary on the next start.

The propeties of pump gasoline change quickly today, I mean a matter of months and today's pump gas goes sour. We used to have to convoy home from the Alliance Ohio Oldsmobile show in August. Someone or more then one guys cars would crap out and not re start with year old or older gasoline in the tank now boiling in the fuel system. Some guys absolutely will not use a electric fuel boost pump even after a hot day failure like this. Same with coming home from Lansing.

My own 1966 3X2 job will certainly have a rotary vane type electric fuel boost pump at the tank for situations as discussed here, on the chance it may have today's gas on a hot day. Good luck and always carry a fire extenguisher.