Carburetor heat shield

[rclenhardt]

I am in need of a carburetor heat shield for my 1973 Mustang 351C 2 barrel carburetor. Anyone have a line on where to get one?

 

[Stanglover]

I'm not too familiar with 73's, but I can offer what I needed to do on my 71 4v.
I was suffering a lot of fuel vaporization in a Holley 670 carb. There was two things I did.
1) block off the exhaust heat cross over passages in the manifold. These were there as a way to warm the carb in cold start up.
2) added a 1" thick fiber spacer under the carb. Spacers are available in different thicknesses, but as I was making my own anyway I opted for thicker to also help airflow (supposedly).
I think there are intake gaskets available with metal inserts that cover the heat ports, but some have just used a thin .020" or less steel under a stock gasket.
I went the whole hog and actually inserted 1/16" SS plates into the manifold cross over ports. I had earlier inserted 5/16" set screws into the carb port openings. That helped but not a total fix.

A heat shield might help if that is the easiest thing, but most of the heat is coming through the cross over ports.
Here's a pic of my 4V manifold that shows what the under carb heat ports look like. I don't know if the 73 intake is similar

 

[Sheriff41]

Check out coolcarb.com

 

[rclenhardt]

Thanks for the input. I found a 1" phenolic OEM carb spacer. Will this work to reduce the heat to the carb?

 

[Paul M]

I am in need of a carburetor heat shield for my 1973 Mustang 351C 2 barrel carburetor. Anyone have a line on where to get one?

I've seen them before on Ebay. I went with the Offy 360 aluminum intake that fit under my Ram air. I was looking for heatshield & found out it was vapor locking before it got to the carb. It acted as if it was running out of gas, which it actually was. It happened on a couple of hot days in a row after getting the motor hot after driving around. This simple little set up stopped it completely. The fuel line routing seemed to be riding on the heater hoses & front of the motor. You need a lil separation along with an aluminum shield between it. Even if you just wrap a strip around the hose for a few inches. I just used some tin snips a pc of aluminum and cut a small rubber hose for edge guards.

​

 

[basstrix]

Thanks for the input. I found a 1" phenolic OEM carb spacer. Will this work to reduce the heat to the carb?

Yes, it's a very good insulator. The thermal conductivity of aluminum is about 170 W/m-K vs 0.3 for G3 (a type of phenolic material). That's says heat will transfer coefficient is more than 600 times greater than G3 phenolic for the same thickness/distance.

 

[Fabrice]

Another option if your vapor lock issues percist, is to install an electric fuel pump, a return line and a regulator. Where the regulator outlet is close to the carb inlet. Pump needs be just above the 14 psi, like 20. Ensuring a constant circuit of cool fuel.
You could as well I think use the existing pump in block if its diaphragm is healthy ( which you can test) And probably use the vent line that is on all 73 as well if in good state and you do not use the egr/canister. The returned flow for carb low pressure being ok for the line diameter. Basically a mimic of injection circuit which never or barely suffer from vapor lock.

 

[rclenhardt]

I've seen them before on Ebay. I went with the Offy 360 aluminum intake that fit under my Ram air. I was looking for heatshield & found out it was vapor locking before it got to the carb. It acted as if it was running out of gas, which it actually was. It happened on a couple of hot days in a row after getting the motor hot after driving around. This simple little set up stopped it completely. The fuel line routing seemed to be riding on the heater hoses & front of the motor. You need a lil separation along with an aluminum shield between it. Even if you just wrap a strip around the hose for a few inches. I just used some tin snips a pc of aluminum and cut a small rubber hose for edge guards.

​

I can't see in the picture where the aluminum piece is installed?

 

[Don C]

Vapor lock generally occurs before the fuel pump. Fuel under pressure vaporizes at a much high temperature than fuel under a vacuum. Fuel line routing along the exhaust is the usual reason for vapor lock. An electric pump as close to the tank as possible will provide pressure for the length of the fuel line.

 

[Stanglover]

Thanks for the input. I found a 1" phenolic OEM carb spacer. Will this work to reduce the heat to the carb?

You should also raise the bracket that holds the throttle cable so that it is at the same angle as the original, or close to it.
If you read my post on breaking another throttle cable, this was something I overlooked earlier, but fixed it now.

 

[sevian87]

Vapor lock generally occurs before the fuel pump. Fuel under pressure vaporizes at a much high temperature than fuel under a vacuum. Fuel line routing along the exhaust is the usual reason for vapor lock. An electric pump as close to the tank as possible will provide pressure for the length of the fuel line.

Are you saying I don't need to do this spacer?

I'm currently having issues warm-starting my car (Florida heat doesn't help) and currently look for some solutions. I am new to carbs, so a part of me just want to go right to EFI

 

[Don C]

You should use the insulating spacer, this helps to prevent fuel percolation, which is different than vapor lock. Fuel percolation is basically fuel boiling in an overheated carburetor, causing the fuel to flow into the intake manifold, causing a flooded condition, making the next start difficult. It can be helped by pressing the accelerator pedal all the way to the floor to introduce as much air as possible into the intake manifold. Do not pump the accelerator pedal.

 

[sevian87]

You should use the insulating spacer, this helps to prevent fuel percolation, which is different than vapor lock. Fuel percolation is basically fuel boiling in an overheated carburetor, causing the fuel to flow into the intake manifold, causing a flooded condition, making the next start difficult. It can be helped by pressing the accelerator pedal all the way to the floor to introduce as much air as possible into the intake manifold. Do not pump the accelerator pedal.

Ah that could be the problem as well. I was pumping 2-3 times before each start, regardless of engine temp. I was watching some videos and it seems that for warmed engines, no pumps may be required or maybe the 1 (long?) pump needed?

For the spacer, what info do I need to find in order to find one? This is not the original engine, although period correct 302 (67-72 was guessed).

 

[Steve McMahan]

Another thing not mentioned is that your fuel pump may be failing. While not as likely as fuel vaporing in the feed line from the tank, unless the line is very close to the exhaust pipe, it’s unlikely that. The Ford service manual has a test you can do to verify the pump. The spacer will help, no mater what else is wrong. But if this just started after being fine before, it’s likely something else changed. Just more food for thought.

 

[Don C]

Ah that could be the problem as well. I was pumping 2-3 times before each start, regardless of engine temp. I was watching some videos and it seems that for warmed engines, no pumps may be required or maybe the 1 (long?) pump needed?

For the spacer, what info do I need to find in order to find one? This is not the original engine, although period correct 302 (67-72 was guessed).

One of these thick gaskets are fairly effective and don't require longer carburetor mounting studs or dealing with the air cleaner not having clearance under the hood.:
https://www.npdlink.com/product/gasket-carburetor-mounting/107152/200957

A phenolic spacer is better, but usually require longer carburetor mounting studs or bolts and may raise the air cleaner too high for hood clearance.
https://www.summitracing.com/parts/hly-17-72?rrec=true

 

[71coop]

It may not be pre-pump vapor lock. temps in the engine bay can be pretty hot, and fuel can boil off between pump and carb with the same result.

When I had my old hot-rod vette, I fought issues with gas boiling between the mechanical pump and carb. Newer fuels are more prone to heat-related issues with the 10% ethanol mist most stations sell. Not debating gas quality, there have been a lot of improvements over the years, but the boiling point is slightly lower, and with some cars, that makes it borderline too low.

I now do both of these with any car just to make sure I don't have fuel boiling problems, whether I need them or not.

I found 2 things that worked well in combination:
1 - a fuel return line routed from the carb inlet. This allowed the boiling fuel to vent off pressure, cool down and return to the tank. Most importantly, it and kept liquid fuel in the carb
2 - A heat shield or a phenolic spacer to keep the carb temp a few degrees lower, to help the now-cooler liquid gas to remain in liquid form

I kept my mechanical pump with this setup - the worst thing about it is a little fuel line fabrication is needed. Also a side note, make sure your gas supply line isn't resting against the block or something that can transfer heat into it.

An additional factor to pay attention to is timing. too little can add a few degrees to the engine's running temp, and exacerbate heat-related issues. even 2 degrees can make a difference, so don't be afraid to play around with that too.

 

[InjectedMach]

Are you saying I don't need to do this spacer?

I'm currently having issues warm-starting my car (Florida heat doesn't help) and currently look for some solutions. I am new to carbs, so a part of me just want to go right to EFI

Go efi

 

[sevian87]

Another thing not mentioned is that your fuel pump may be failing. While not as likely as fuel vaporing in the feed line from the tank, unless the line is very close to the exhaust pipe, it’s unlikely that. The Ford service manual has a test you can do to verify the pump. The spacer will help, no mater what else is wrong. But if this just started after being fine before, it’s likely something else changed. Just more food for thought.

Thanks for the insight! I bought this mustang about 3 months ago, and with the wonderful daily rains and just life in general, have really only driven it a handful of times so far. Most of the drives have been just cruising around, no stops, so I have no idea if this is really a "new" issue as I am still learning this car's quirks, and well old mustangs all-together!

 

[sevian87]

One of these thick gaskets are fairly effective and don't require longer carburetor mounting studs or dealing with the air cleaner not having clearance under the hood.:
https://www.npdlink.com/product/gasket-carburetor-mounting/107152/200957

A phenolic spacer is better, but usually require longer carburetor mounting studs or bolts and may raise the air cleaner too high for hood clearance.
https://www.summitracing.com/parts/hly-17-72?rrec=true

I can probably measure and check what kind of clearance is available, but will order that first one just in case, thank you!

 

[sevian87]

It may not be pre-pump vapor lock. temps in the engine bay can be pretty hot, and fuel can boil off between pump and carb with the same result.

When I had my old hot-rod vette, I fought issues with gas boiling between the mechanical pump and carb. Newer fuels are more prone to heat-related issues with the 10% ethanol mist most stations sell. Not debating gas quality, there have been a lot of improvements over the years, but the boiling point is slightly lower, and with some cars, that makes it borderline too low.

I now do both of these with any car just to make sure I don't have fuel boiling problems, whether I need them or not.

I found 2 things that worked well in combination:
1 - a fuel return line routed from the carb inlet. This allowed the boiling fuel to vent off pressure, cool down and return to the tank. Most importantly, it and kept liquid fuel in the carb
2 - A heat shield or a phenolic spacer to keep the carb temp a few degrees lower, to help the now-cooler liquid gas to remain in liquid form

I kept my mechanical pump with this setup - the worst thing about it is a little fuel line fabrication is needed. Also a side note, make sure your gas supply line isn't resting against the block or something that can transfer heat into it.

An additional factor to pay attention to is timing. too little can add a few degrees to the engine's running temp, and exacerbate heat-related issues. even 2 degrees can make a difference, so don't be afraid to play around with that too.

I appreciate the info, I haven't yet had the chance to track the fuel line and see where it goes/touches.

Definitely working on getting a spacer, seems to be the main suggestion for the most part, so I'll start there and see where it goes. I noticed you said you left it a mech fuel pump, would an electric pump solve/lessen this issue?