Hot Rods Vapor lock/percolation. Its too damn hot

YES! YES!


Ben

 

Vapor lock was not unheard of before unleaded gasoline containing ethanol became commonplace.

 

I have a Phenolic spacer, holley aluminum heat shield, rubber isolator, and my fuel line wrapped with DEI heat wrap. Still have boiling after shutting it off and letting it sit on hot days but not so bad it won't start. Next I'll be louvering the hood.

 

My 80,000 km engine still had the cross-hatch visible in the cylinders. 36,000 km of mostly highway miles with a 160°F thermostat later I had the heads off, still has a nice cross hatch in the cylinders.

I know you've been repeating this info occasionally for several years here. While I don't think the info you have from Summit is wrong, I think it's more telling that they don't seem to publish it anywhere anymore.

This currently available help article from Summit Racing tells a little more accurate story, I think.

https://help.summitracing.com/knowledgebase/article/SR-05284/en-us#:~:text=For daily drivers, coolant temperature,move around and wear faster.


Particularly the last part applies to us:

If your car is a basically stock daily, a 195°F thermostat is probably the ticket, but if you're worried about running a 160°F thermostat in your fun car because of accelerated cylinder wear, you'll most likely not own the car anymore when that becomes an issue. As long as you warm up your fun car before you beat on it or do any significant speeds, you shouldn't have much concern.

 

I have the same setup. Mine tends to reveal itself just as I start moving after being parked or sitting a the stop light, when it surges due to vapour lock. My truck also has a return line from the mechanical pump. In my experimentation, when I take the hood off the vapour lock all but goes away. Once you're moving continuously, there are no issues. The heat getting trapped under the hood is what allows the fuel to boil in the carb on mine. Getting that air out does wonders.

 

I’m running a mechanical pump with return line on my 500. No issues with vapor lock.
There is a fuel filter with a return line that would help

 

Like the one that @anthony myrick shows but made for a 427 Corvette so it costs more. There's comfort in that

 

Pontiacs had issues right from the factory due to the fuel line routing in the engine bay.

 

1/2" phenolic spacer is good if you have room for it. On my TA's it lifted the shakers up too far so I used this type. It did the job.

 

GM used the fuel return system on ‘60s vehicles from Corvette to Cadillac. A insulating carb spacer and installing a fuel return solved my vapor lock symptoms. An electric fuel pump also cures a lot of issues if installed properly.

 

I don't know where everyone is talking about vapor lock. The OP is talking about percolation (fuel boiling in the carb). Especially when the car is turned off in hot weather, flooding the engine. The things mentioned in my post address this, which has nothing to do with vapor lock.

 

Circulating fuel back to the tank keeps the fuel temp lower.
So it’s cooler when it gets to the carb.

 

I think there's a lot of confusion as a result of not understanding that vapor lock only occurs on the inlet side of the mechanical fuel pump. Stock mechanical fuel pumps, even in working condition, are not designed to pull air bubbles thru the fuel inlet pipe from the tank. They are not an air vacuum pump. They must have an ample supply of purely liquid fuel which they can compress and discharge to the pump outlet to feed the carburetor. Once the liquid fuel leaves the pump under pressure it will easily displace any air in the fuel outlet pipe between the pump and the carburetor.

Fuel percolation can still occur in the float bowl and fuel line from the pump and cause a flooding condition. But that's a different condition than vapor lock.

 

Me no think they are listening too good to you, Senior.

 

I’m no scientist
The return has kept mine from hiccuping
My mechanic buddy credits a return line and no fuel bowls for this not being an issue for EFI.
We had a Holley with a bad boiling issue.
Ran a return line and it stopped. I don’t know
I just did what the boss said.

 

The OP did mention the possibility of vapor lock.

 

https://www.carparts.com/details/Ho...ecd59e2ab5df1a106da3f8541ebbd0eb&gclsrc=3p.ds

 

anymore potential solutions to carburetor gas boiling? going to get up to around 107 degrees by end of coming week in Sacramento, CA area

 

>>anymore potential solutions to carburetor gas boiling?>>

Amazon's choice. Pretty good reviews too.

 

You might want to consider putting a fuel pressure gauge in the line before the carb to see what your pressure is. Even factory stock fuel pumps can occasionally run much higher than your carb is designed to handle, and I've seen more than a couple be up around 9psi. If it shows high pressure then simply install a pressure regulator and adjust it down around 4.5-5 psi and likely this issue will disappear.
I put pressure regulators on everything I build whether they're electric or mechanical fuel pumps, just to avoid any issues.

 

Believe or not but here in So Cal it gets hot. I was getting bad vapor lock. (car stalling after about 20 minutes) I did the old Clothes pins on the fuel line. Haven't had VL since. Its been years.

 

Wood is an insulator, there's no way adding them to a fuel line could help cool the line. I did buy a car one time that had metal clothes pins on the fuel line, that could shed some heat, at least in theory.

 

> > Wood is an insulator, there's no way adding them to a fuel line could help cool the line. > >

Sure it can. Insulators help keep things cool or warm, cold or hot. Lotsa clothespins needed. Cork's good too. 8^)

 

Most people put 1 or 2 on the fuel line.

 

Better call your AA sponsor.

 

This place is about cars. If we have to call anybody, we call AAA!

 

Just out of curiosity, did you place them on the inlet or outlet side of the fuel pump, or both?

 

The real challenge is the open engine compartments with the carb bowls getting direct sunlight

 

I've battled this issue of boiling for years and tried most of the fixes mentioned here. They all help but It's damn hot and my car is black too! Vapor locked just last week right before I turned off back to my house. Luckily this time it restarted pretty easily with the electric pump, but it was really cycling fast.
I would like to find some finned fuel line to try from the pump to the filter on mine. It's a vertical run and the fan blows right on it. I used to own a 74 Bronco with Pwr steering, a 302 v8. It had a finned section of tubing that seems like it could be adapted as a section of fuel line. I'm on the hunt for one to try out. Mine also still has a glass bowl filter so you can watch the fuel bubble easily.

Sorta like this. But I would want it to have threaded ends not hose clamps

I know Perma-cool makes a cooler that may adapt as well.

 

You might have better luck with Uber or Lyft.