Heat soak - your tips and tricks

[WFarm]

I had a similar problem with my Blazer when i first got it. The engine is a 71 454 from a Chevelle with an Edelbrock carb, Weiand aluminum intake and factory cast iron exhaust manifolds. It would start right up, but on real hot days if you drove it up to temp (around 200 deg F) and then parked it for a few minutes (or even slowed way down in traffic) it would fart and cough and then just die. There was no restarting it until it had cooled off for 45 minutes to an hour. Carb and the mechanical fuel pump would be too hot to handle. Once it did restart you had to cross your fingers to get it back home before it stalled again. First time it did this it cost me a tow since I didn't know yet what I was dealing with. A huge hint was when it immediately fired up once home.

After making my changes it has been trouble free. A couple weeks ago when we had a heat wave here and temps were in very high 90s with heat index around 120. I gave it a "torture test" where I drove it and parked it for 20 minutes, started it up and drove more, parked again..wash, rinse, repeat. It worked great.

Heres what i did.

1) Installed heat shield and phenolic spacer under the carb.
2) Re-did fuel lines, making new lines from CUNI and routing them away from the engine. Insulated these lines.
3) Restored fuel return line.
4) Installed electric pump back at tank.
5) Removed the mechanical pump from the engine, installed block off plate.
6) Run 90 octane non-ethanol gas.

Items 1-3 by themselves did not do the trick. In the end changing to an electric pump, in conjunction with restoring the return line was what did it.
As a sidenote, had the same issue a few years back with my 1957 Chevy, running a 383 Stroker with a Holley carb. In that case insulating the carb was sufficient and I did not have to go to an electric fuel pump.

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[Grit dog]

Spitballing a little here. If for no other reason than throwing parts at it in Scandinavia is likely quite expensive.
Maybe do a little empirical heat test. You know how it acts when hot and how long it takes to cool down. Drive it home, hot. Immediately open hood and blow a fan on the engine. Could repeat the same with a water mist. Point being if you cool it X amount faster does it solve the problem?
@WFarm did a great job of explaining all the basic workarounds. As mentioned you may not need as much as it may no get quite as hot there.
I could see putting a lift pump on it as a last resort. I’d rather keep a wholly mechanical system though if I’m dealing with simplicity.

 

[Chevy 88]

Here is what I run:

Amazon.com: 2" Tall Ported Phenolic Carburetor Spacer Compatible with Holley 4150/4160 4bbl SBC BBC Carb

Amazon.com: 2" Tall Ported Phenolic Carburetor Spacer Compatible with Holley 4150/4160 4bbl SBC BBC Carb

www.amazon.com

 

[Matt69olds]

What kind of mechanical fuel pump?

If it’s just a 2 line setup (supply line from the tank to the pump, and pump to the carb) make the fuel return functional. A factory pump for a truck with A/C will have the fuel return fitting with the tiny orifice in the return line. If it’s a aftermarket pump, you will have to fabricate a “T” in the pump to carb line, and install a fitting with a tiny orifice and connect that to the factory return line.

The return system was originally designed to constantly circulate fuel thru the pump back the the tank. That kept the pump and fuel cooler. The other advantage is it allows the fuel to vent after engine shutdown. During heat soak, the fuel in the pump and lines will absorb radiant heat. The fuel boils, the pressure rises enough to push the needle off the seat in the carb, the engine floods, causing a hot restart.

 

[Sad Sack]

Here is what I run:

Amazon.com: 2" Tall Ported Phenolic Carburetor Spacer Compatible with Holley 4150/4160 4bbl SBC BBC Carb

Amazon.com: 2" Tall Ported Phenolic Carburetor Spacer Compatible with Holley 4150/4160 4bbl SBC BBC Carb

www.amazon.com

Got your name all over it!

Amazon.com: M2 Machines 1973 Chevy Cheyenne Super 10 Square Body Bedless Truck Bright Red w/Graphics Ltd Ed to 3550 pcs 1/24 Diecast Model Car 40100-HS02 : Arts, Crafts & Sewing

Amazon.com: M2 Machines 1973 Chevy Cheyenne Super 10 Square Body Bedless Truck Bright Red w/Graphics Ltd Ed to 3550 pcs 1/24 Diecast Model Car 40100-HS02 : Arts, Crafts & Sewing

www.amazon.com

 

[SquareRoot]

What are the symptoms of the problem?

I'm guessing heatsoak?

 

[hack_man]

I’m not familiar with the Edelbrock carbs. I know a problem with older qjets is that they can leak fuel from well plugs into the motor causing a dry carb and a possible flooded condition, is this possible with the Edelbrocks?

Is this why my truck always takes many cranks to start when it's not been run for a week?
It starts fine in cold weather as long as it's only been a few days, but leave it for a week and it's really hard to start, always been that way.
OEM Quadrajet carb

 

[Ricko1966]

Is this why my truck always takes many cranks to start when it's not been run for a week?
It starts fine in cold weather as long as it's only been a few days, but leave it for a week and it's really hard to start, always been that way.
OEM Quadrajet carb

No that's probably not your problem,wrong fuel filter,leaky needle and seat more likely. The leaky plug well thing was pretty much over late 60s early 70s,when they changed the plugs.

 

[nvrenuf]

Yeah, I don't know when things changed in the qjets, just that it was a problem and epoxying them was commonplace with rebuilders.

 

[hack_man]

Yeah, I don't know when things changed in the qjets, just that it was a problem and epoxying them was commonplace with rebuilders.

I had it rebuilt about 25 years ago by a professional carb rebuilder and told him about the problem, I was hoping the hard start problem (after sitting for days) would go away but it never did.

I can live with it but always wondered what was the cause.

 

[Matt69olds]

It’s today’s fuels.

Way back when everyone had carbureted vehicles, the refineries added chemicals to the fuel to prevent evaporation. Now, everyone drives vehicles with EFI and sealed fuel systems, the additive to prevent evaporation was an added expense that benefited a tiny percentage of buyers.

If it really bothers you, put and electric fuel pump on it. Prime the system before trying to start it.

 

[dd1990]

What kind of mechanical fuel pump?

If it’s just a 2 line setup (supply line from the tank to the pump, and pump to the carb) make the fuel return functional. A factory pump for a truck with A/C will have the fuel return fitting with the tiny orifice in the return line. If it’s a aftermarket pump, you will have to fabricate a “T” in the pump to carb line, and install a fitting with a tiny orifice and connect that to the factory return line.

The return system was originally designed to constantly circulate fuel thru the pump back the the tank. That kept the pump and fuel cooler. The other advantage is it allows the fuel to vent after engine shutdown. During heat soak, the fuel in the pump and lines will absorb radiant heat. The fuel boils, the pressure rises enough to push the needle off the seat in the carb, the engine floods, causing a hot restart.

+1 on making or keeping fuel return line, that cured my vapor lock