How to Prevent Holley Carburetor Fuel Boiling

-
Bonkled_2900

Bonkled_2900

Member
Joined
Aug 23, 2024
Messages
16
Reaction score
1
Location
Idaho
I need to know how to create a type of insulator or something to prevent fuel boiling in the carb. I recently had an issue where I went for a semi-long drive and when I restarted the engine hot it wouldn't start due to boiling gas leaking from the boosters and flooding the engine. I need steps on how to create something to prevent this. Thanks
 
Install a return after the fuel pump so the fuel pressure is not dead ended up against the needle and seat. This will also allow the fuel to circulate and allow fresh fuel to reach the carb that isn't boiling
 
Oldmanmopar said:
Install a return after the fuel pump so the fuel pressure is not dead ended up against the needle and seat. This will also allow the fuel to circulate and allow fresh fuel to reach the carb that isn't boiling
Click to expand...
I need to know how
 
Plymouth 65 said:
Use a phenolic spacer between the carb and intake manifold. 65
Click to expand...
I tried that and even added a heat deflector it didn't help ..

Steve 102.JPG
 
Bonkled_2900 said:
I need to know how
Click to expand...
Not hard at all, buy yourself a new fuel line and install it next to the stocker

Then buy a new fuel sending unit with a return line port (use your old gasket) and plumb the stock line in as the return line

All that's left now is a return style regulator set to 6psi and tie it all together
 
Bonkled_2900 said:
I need to know how to create a type of insulator or something to prevent fuel boiling in the carb. I recently had an issue where I went for a semi-long drive and when I restarted the engine hot it wouldn't start due to boiling gas leaking from the boosters and flooding the engine. I need steps on how to create something to prevent this. Thanks
Click to expand...


How much coolant temperature?

Is the exhaust crossover on the intake open?

Mechanical fuel pump?

The only part I’ve ever seen drop actual carb temp is called “Cool Carb” and it’s two pieces.

I’ve tried every thing you can think of and not one of them ever dropped carb temperature.

To run a return system you need a fuel pressure regulator that has a bypass feature.

Then you have to run a line from that regulator to the tank.

It’s unusual for a Holley to have this issue. Usually it’s when coolant temperatures are above 195 degrees and you have an iron intake manifold with the heat crossover open.
 
Newbomb Turk said:
How much coolant temperature?

Is the exhaust crossover on the intake open?

Mechanical fuel pump?

The only part I’ve ever seen drop actual carb temp is called “Cool Carb” and it’s two pieces.

I’ve tried every thing you can think of and not one of them ever dropped carb temperature.

To run a return system you need a fuel pressure regulator that has a bypass feature.

Then you have to run a line from that regulator to the tank.

It’s unusual for a Holley to have this issue. Usually it’s when coolant temperatures are above 195 degrees and you have an iron intake manifold with the heat crossover open.
Click to expand...
Coolant temp is around 210, Mechanical fuel pump, this never happened before and when we put an octane additive in the fuel this never happened either
 
Part of your problem is where you live.

100 plus in the summer and sub freezing in the winter.

Assuming you drive year around when you can the heat is great on the winter but in the summer it causes issues.

IMO if you get the coolant temp down to 190 it would help.

After that the next fix is to block the crossover off but on cold days it can be a bear when the engine is cold.

If that doesn’t fix it then you can do the return line.

FWIW at this point in time it’s almost getting to be SOP that you need an electric pump and return line.

On top of the minimal alcohol content in pump gas you have the issue that the fuel is formulated for the higher pressure of EFI.

That changes what the fuel acts like in carb’d stuff. The return line is probably the most expensive fix but it’s probably the most cost effective in the long run.
 
Start with having an adequate cooling system. Lose the iron intake manifold and the giant low-hanging air cleaner that holds heat around the carburetor.
I've never had fuel boiling in any carburetor.
 
Bonkled_2900 said:
How would i get the coolant temp to 190?
Click to expand...

That’s another issue that makes the return line more viable.

I don’t know what you have for cooling system components it if your cooling system is capable you can lower the thermostat opening temperature and see if your cooling system will keep up.

It probably will on cooler days. Unless you have a really good cooling system. Then changing the thermostat will lower the coolant temp, providing g the system can keep up.
 
Bonkled_2900 said:
Coolant temp is around 210, Mechanical fuel pump, this never happened before and when we put an octane additive in the fuel this never happened either
Click to expand...
There's your main problem. Get the coolant temp down and I bet your issue will vanish.
 
Bonkled_2900 said:
We have been driving on 80-95 degree days, it’s around 50-60 now hopefully that will help
Click to expand...
I am confident it will and if and when it does, that will verify cooler temps will solve it. I agree 100% about the return helping, too. With the lead gone from the gas and alcohol added in, carburetor engines need some extra things EFI doesn't.
 
Bonkled_2900 said:
We have been driving on 80-95 degree days, it’s around 50-60 now hopefully that will help
Click to expand...


That certainly helps when ambient temperatures are cool like that.

I’ve posted this before but my dad had a 1988 Ford F250 and that was the last year for carbs on that stuff.

It’s tuning, cam timing and induction were so jacked up that it would book the carb dry.

I fought it for a good bit then I pulled the intake off. That giant, heavy pig iron mother.

And the bottom of the manifold was bright blue. A very pretty bright blue.

That means that thing was HOTTER than the hubs of hell. Well, not quite that hot but close.

There was no way the carb could tolerate all that heat.

So I bought a gasket with stainless steel shims to block the heat off to the intake.

That helped a bunch, but the first time I hooked the trailer up and took the car to the races it burned through the shims and by the time I got home that day the carb was again being killed by all that heat.

So I was going to pull the intake back off (I already had it back off to put new shims back in there so at least you could drive it) and I was going to weld the crossover shut.

My dad said piss on it and traded that turd off on an 89 Dodge and that nightmare was gone.

High heat under the carb is a bad thing.

Again, depending on your cooking system it may be cheaper to do the return line.

I hate doing things twice so if it was mine I’d upgrade the cooling system and do the return line.

This is why I lose my mind when guys are putting a car together and they don’t spend enough money on the cooking system.

I’m of the opinion that you should be able to drop a 160 thermostat in to a car and have the cooling system keep up, even when you have to slow roll through downtown hell.

It’s more expensive and time consuming to try an upgrade later.

Know my criticism is pointed at you. It’s at those guys who think this **** doesn’t matter when it does.

You can’t get a cooling system too good. You can’t. That’s why God gave men brains to develop stuff like a thermostat that makes it so you can control the cooling system.
 
Newbomb Turk said:
That certainly helps when ambient temperatures are cool like that.

I’ve posted this before but my dad had a 1988 Ford F250 and that was the last year for carbs on that stuff.

It’s tuning, cam timing and induction were so jacked up that it would book the carb dry.

I fought it for a good bit then I pulled the intake off. That giant, heavy pig iron mother.

And the bottom of the manifold was bright blue. A very pretty bright blue.

That means that thing was HOTTER than the hubs of hell. Well, not quite that hot but close.

There was no way the carb could tolerate all that heat.

So I bought a gasket with stainless steel shims to block the heat off to the intake.

That helped a bunch, but the first time I hooked the trailer up and took the car to the races it burned through the shims and by the time I got home that day the carb was again being killed by all that heat.

So I was going to pull the intake back off (I already had it back off to put new shims back in there so at least you could drive it) and I was going to weld the crossover shut.

My dad said piss on it and traded that turd off on an 89 Dodge and that nightmare was gone.

High heat under the carb is a bad thing.

Again, depending on your cooking system it may be cheaper to do the return line.

I hate doing things twice so if it was mine I’d upgrade the cooling system and do the return line.

This is why I lose my mind when guys are putting a car together and they don’t spend enough money on the cooking system.

I’m of the opinion that you should be able to drop a 160 thermostat in to a car and have the cooling system keep up, even when you have to slow roll through downtown hell.

It’s more expensive and time consuming to try an upgrade later.

Know my criticism is pointed at you. It’s at those guys who think this **** doesn’t matter when it does.

You can’t get a cooling system too good. You can’t. That’s why God gave men brains to develop stuff like a thermostat that makes it so you can control the cooling system.
Click to expand...
Thank you for that, I just found out i have a 195 thermostat on the car
 
Bonkled_2900 said:
I need to know how to create a type of insulator or something to prevent fuel boiling in the carb. I recently had an issue where I went for a semi-long drive and when I restarted the engine hot it wouldn't start due to boiling gas leaking from the boosters and flooding the engine. I need steps on how to create something to prevent this. Thanks
Click to expand...
Is this the first time you had this problem? Have you been driving it all summer and this was the first event like this? How old is your gas?
 
BSB67 said:
Is this the first time you had this problem? Have you been driving it all summer and this was the first event like this? How old is your gas?
Click to expand...
First time this happened, drove all summer and we had just filled the gas the day before
 
Oldmanmopar said:
I tried that and even added a heat deflector it didn't help ..

View attachment 1716302337
Click to expand...

Had the same issues with an Edelbrock carb, I’m sure you know why.
Added a return T’d right at the carb inlet and an inline restrictor orifice for the return that keeps the main line pressure around 6 pounds.
When choosing the restrictor I used a gauge to show the main line pressure.
No return regulator needed.
Running the same system with the Holley thats been on there for a few years now.

Fuel boiling is a pain in the backside.
 
Seems a bit strange that you didn’t have problems all summer before now. Was it hotter than usual?

Possible that you got a batch of winter fuel with a higher RVP? I believe the switch date is September 15. This has happened to me on hot days near the 6/1 and 9/15 transition dates having the high RVP fuel on hot days with a long engine run.

Knowing this, I work around it.
 
Last edited:
You must log in or register to reply here.
-

Back
Top