preventing fuel from boiling in the carb

[Belgian1979]

Guys,

When running a carb I've seen numerous issues with the carb getting heat soaked after shutting the car down for a short time and then restarting. Not sure what happens, but I assume that the lead free fuel starts to boil in the carb due to it getting heat soaked and the vapours ending up in the engine causing it to be flooded.
I have once already tried a plastic carb to manifold spacer but it did help only marginally.
One of the things that play a role is that the heat seems to stay under the hood of the car. (low hood line)

PS the carb is used in conjunction with a drop base aircleaner to get the thing under the hood.

Any suggestions how to get around this.

[GRTfast]

Guys,

When running a carb I've seen numerous issues with the carb getting heat soaked after shutting the car down for a short time and then restarting. Not sure what happens, but I assume that the lead free fuel starts to boil in the carb due to it getting heat soaked and the vapours ending up in the engine causing it to be flooded.
I have once already tried a plastic carb to manifold spacer but it did help only marginally.
One of the things that play a role is that the heat seems to stay under the hood of the car. (low hood line)

PS the carb is used in conjunction with a drop base aircleaner to get the thing under the hood.

Any suggestions how to get around this.

Do you have a return line going back to the tank after the carb? Usually if you have a dead head setup, the fuel is under the hood for a long time and gets hot enough to boil. You want to keep the fuel moving.

[Belgian1979]

The car has a return line on the fuel pump but not on the carb line.

[ClassAct]

Cool Shield is what you want. I’d you can, run the shield and spacer. It’s the ONLY heat shield I’ve ever used that actually works.

And block off the exhaust crossover if you have it. You don’t need it.

[ClassAct]

Sorry, here is the link to the company. http://www.coolcarb.com/order-products.html

[rp930]

I’m using one of these right now and it is working well.

https://www.jegs.com/p/Holley/Holley-In ... 3/10002/-1

[rebelrouser]

Not sure what engine you are dealing with, but all the old muscle car engines I do I block the exhaust heat crossover passage. Even on regular restorations, the alcohol content of today's fuel, makes them really prone to fuel boiling and vapor lock. I have noticed that the AFB's seem really prone to this problem, I guess since the primary material is aluminum and not pot metal, they soak up more heat? I also try to use a thicker carb gasket as well. Just messed with a 68 AMX and we finally just installed a small electric push pump back at the fuel tank to fix it. He could drive it all day with no problems, but if it heat soaked for say 45 minutes, it would not start until it cooled off.

[skinny z]

Are you using a mechanical fuel pump?
If so, these pump insulators have shown to be effective.

www.summitracing.com/parts/ctr-85-000

https://www.summitracing.com/parts/ctr-85-010

[GRTfast]

Are you using a mechanical fuel pump?
If so, these pump insulators have shown to be effective.

www.summitracing.com/parts/ctr-85-000

https://www.summitracing.com/parts/ctr-85-010

I use this mechanical pump insulator, I have a restricted return line after the fuel log. Also, a 1 inch phenolic spacer under the carb. Seems to work fine and I drive in FL summers.

https://www.summitracing.com/parts/sit- ... gLoTfD_BwE

[chimpvalet]

Would it help to run an electric pump and kill that a short time before engine shutdown? That method seemed to help when running DCOE Webers.

[steve cowan]

I run a holley mechanical fuel pump fed by -10,
-8 from pump to fuel log then dash 8 to return bypass on firewall then back to the tank with zero bypass restriction,
Our drag racing here in Australia starts in February which for us is the nastiest month of the year 40 degrees Celsius plus lots of humidity.
I also have my braided fuel lines inside thick foam insulation like you see on air conditioners which I think helps,I also fed my main fuel line through the chassis hopefully to try and stove off some radiated heat from the road.
I like that insulation tray under carb

[Belgian1979]

Yes mech fuel pump.
Car is a C3 Corvette, so not much underhood ventilation.

[BigBlocksOnTop2]

Same problem here. Fixed by making and silver brazing a AN4 fitting on the secondary carb feed line. Put an orifice ( 6-32 brass set screw) in this fitting .040 to allow some fuel to recirc. to the tank. That feed line on the carb got hot and I believed it allowed fuel to percolate. After the modification the line got warm, but not hot to the touch. It worked.

[1972ho]

If you can try insulating as much of your fuel as you can with some of the insulation that Home Depot sell for a/c systems it will help.

[JES]

Make your own "heat shield" it's actually a heat sink. From .080 aluminum, like those in the first link about mid way down. Make it as big as you can. I have mine made up by a local fab shop in mutipuls at a time for savings. But just spend the time to cut it out by hand for just one. It will lower carb temps approximately 10- 12 degrees. In most cases that's all you need.