Stalling in heat help

[Mgicm]

People in this forum have helped tremendously on some other issues Ive had and hoping this one will be met with the same help. At my wits end. let me explain.

Have a 73 GMC step van.. 3/4 ton underneath. 350 sbc with edelbrock carb. HEI. So last year when it was over 90 degrees out, i would get some backfire occasionally in carb..like pops. Changed over to HEI and new carb. Seemed fine. Then we would take a run on highway say 30 miles and when we got off highway to a stoplight, it would stall. Temp gauge in middle so didnt seem to be overheating. Check radiator and overflow..all good. Ended up changing distributor 3 months ago as mechanic said it was coming up as bad on his tests.

Fast forward to now the middle of summer. Today was hot.. 92 degrees. Drove to a destination about 30 miles away. Drove perfect..mostly highway but some local miles/stoplights. Got to destination and parked the van for 2 hours.

Tried to start and it stalled out. Got started, drove back on the 30 mile route and there was tons of traffic. Stalled out about 20 mins into our drive back. Could not restart it. Opened the hump inside stepvan to let heat out. Started after waiting about 15 - 20 mins. Got some miles in on open highway for 15 mins. Then back to traffic but now i have hump open inside to let heat out. Stalled again but was able to start it quicker this time. Bumper to bumper traffic all the way home but kept it running. Get home , shut it off and it is running/bucking/dieseling/popping for a good 15-20 seconds after I shut key.

So my guesses vary here as to where the issue is. Gas boiling in carb/vapor lock? Timing wrong/running too hot? Engine compartment too small for such heat of motor? Fan not working as expected? Distributor bad again? Gas line too close to motor and boiling in traffic/heat?

Anyone have thoughts or opinions? Bringing to mechanic but want to have some sort of education behind me . Sure appreciate!

[nonstop]

What kind of carburetor are you running and is your HEI running on 12 volts, or with the points resistance wire?

Also curious as to what your timing is.

[Mgicm]

To be honest I would need to recheck. Not sure about the wire.. might you tell me what you ask or why it matters..trying to learn. Thanks

[nonstop]

Sure thing! Points ignition uses a resistance wire, which lowers the voltage to the points to prevent them from burning out. HEI needs a full 12 volts from a 12 gauge wire or so. Po voltage has caused many ignition problems, and your problem is going to either be fuel or ignition related at this time. The reason I ask about the carburetor is the fact that that truck ran for 44 years with that engine compartment. GM also put big blocks and Diesels in the same compartment. So, unless there is something different from the stock set up, in terms of fuel line routing, carburetor or something of the like, I am not overly convinced it is vapor lock.

[Dead Parrot]

Did you set the carb float levels according to the install instructions? For some reason, most edelbrock carbs leave the factory with bad float levels.
Check your fuel filter(s).
Check the heat riser valve if equipped. A stuck one can cause too much crossover exhaust and can overheat and damage a carb.
How many blades on the fan? Is the fan clutch working properly?
A points distributor normally ran on 6V and got the full 12v when the key was turned to start. An HEI distributor wants 12v full time. If you still have the resistance wire/block resistor the points coil used, might explain why your HEI failed the first time.
BTW, here, this time of year we call 92 a cool wave.

[Mgicm]

We had the same thought. Truck ran for 40.years and while I don't know the history, I assume this was not an issue. The ignition was changed as it always had issues starting the van. Even so much that the previous owner had some.sort of button installed on dash and told me to use it if key didn't start it. I did have to use it sometimes but not since he was installed.

I do remember it sputtering at times on hot days before hei...a lot of popping in carb too. But no stalling like this. Today I got to a light, sat for like 2 minutes at light. then drove for the next minute with about 10 different sputters meaning like carb popping and truck not going much.. almost like it is starved of gas. If I leave it ideal in driveway for a few minutes it always sputters for a minute or two then drives fine.

Truck.does have a 30 gallon aftermarket tank in a side compartment that is built into body. So I would think since it's on side, it is not using much or all of the original fuel line. Maybe it was routed differently than original? The tank is on passenger side with a hose coming out of bottom to the carb. I have not fully traced it yet...not checked fuel filter. But on open highway I get not even a hesitation or blip...runs perfect. Only when in traffic or at a light foes it give trouble.

[mongocanfly]

^^^I agree^^^ check that your fuel lines arnt to close to the exhaust.... causing vapor lock...

[old Rusty C10]

also check to make sure youre not too close with wires to exhaust like on the harness