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Last year I put a brand new 750 carb on my vet.(427/435). I have a guage that goes into the chrome metal line that i got from summit. I heard that when it gets real hot outside that carbs run like garbage but it was 70 degrees in Chicago this weekend and I drove the car and when I got into a little traffic and the car would heat up it was hard to keep the car running. If I gave the car gas it would die out. I do not know whether I should get an aluminum radiator with electric fans or is it because the fuel pressure guage is only reading 4psi. I know that it should be at least 6psi but when the car is not in traffic it was fine. it was just embarassing to have the car cut off under a bridge in traffic with the top down. Any suggestions.
 

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DC Crew
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Probably vapor lock. As a diagnostic tool, put clothes pins from the pump to the carb. They will dissapate heat and keep the vapor lock from occuring. If it fixes the problem, the heat is usually picked up at the lower radiator hose area. Try to eliminate the hose heat from being absorbed by the fuel. A lot of this is caused by the shitty fuel we are buying. Lower flash point pressure!

Let us know! :thumbsup:
 

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Two potential things I can think of:

A) Do you have a heat sheild between the carb and manifold? The heat radiating up from the engine may be boiling the gas in your float bowls. This is not uncommon with Holleys & Edelbrocks (& others I'm sure).

2) Does your fuel pipe from the pump touch the engine anywhere? If so, tweek it away. Is your fuel pipe wrapped with insulation? If not, heat soak could be a problem boiling the gas in the pipe. ("Vapor lock")

A not uncommon problem I have suffered from is "flash over": When the engine is hot and I stop for a short while, the gas in the fuel pipe soaks a lot of heat from the engine. Being under a bit of pressure, between the check valve of the fuel pump and the needle valve in the float bowl, it will not boil but it gets very hot. When I started the motor and promptly roared away without letting it run a few moments, it would stall. The problem is that the engine will run at idle for a few moments on the fuel in the float bowl, but upon acceleration, the level quickly drops, the needle valve opens quickly, and the hot fuel rushes into the float bowl which is at atmospheric pressure where it flashes into steam. Not only does this vapor not replenish the liquid fuel level, but because it is flashing to vapor, it blows the low level of liquid fuel away from the jet wells causing fuel starvation and stalling.

Before you go replacing the radiator, investigate fuel delivery/temperature.

John
 

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Discussion Starter #5
Two potential things I can think of:

A) Do you have a heat sheild between the carb and manifold? The heat radiating up from the engine may be boiling the gas in your float bowls. This is not uncommon with Holleys & Edelbrocks (& others I'm sure).

2) Does your fuel pipe from the pump touch the engine anywhere? If so, tweek it away. Is your fuel pipe wrapped with insulation? If not, heat soak could be a problem boiling the gas in the pipe. ("Vapor lock")

A not uncommon problem I have suffered from is "flash over": When the engine is hot and I stop for a short while, the gas in the fuel pipe soaks a lot of heat from the engine. Being under a bit of pressure, between the check valve of the fuel pump and the needle valve in the float bowl, it will not boil but it gets very hot. When I started the motor and promptly roared away without letting it run a few moments, it would stall. The problem is that the engine will run at idle for a few moments on the fuel in the float bowl, but upon acceleration, the level quickly drops, the needle valve opens quickly, and the hot fuel rushes into the float bowl which is at atmospheric pressure where it flashes into steam. Not only does this vapor not replenish the liquid fuel level, but because it is flashing to vapor, it blows the low level of liquid fuel away from the jet wells causing fuel starvation and stalling.

Before you go replacing the radiator, investigate fuel delivery/temperature.

John

A. No Heat sheild
B. The Line is not touching the engine but it is not wrapped in insulation.

I have to put a new fuel pump on the car because I am not pleased with the pressure. I just put the mighty demon on last year so do you suggest that I run a braided line from the pump into the carb along with a heat sheild. I appreciate the reply back as well(you too RJENT) because this really bothered me this weekend
 

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A. No Heat sheild
B. The Line is not touching the engine but it is not wrapped in insulation.

I have to put a new fuel pump on the car because I am not pleased with the pressure. I just put the mighty demon on last year so do you suggest that I run a braided line from the pump into the carb along with a heat sheild. I appreciate the reply back as well(you too RJENT) because this really bothered me this weekend
Just remember a braided line is really a rubber line with a braid around it. Carry a fire bottle-- a BIG one.
 

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DC Crew
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A. No Heat sheild
B. The Line is not touching the engine but it is not wrapped in insulation.

I have to put a new fuel pump on the car because I am not pleased with the pressure. I just put the mighty demon on last year so do you suggest that I run a braided line from the pump into the carb along with a heat sheild. I appreciate the reply back as well(you too RJENT) because this really bothered me this weekend
Vapor lock is common on these cars. They pick up heat from the engine and cooling system.

I agree with timAT, I would be very carefull about using braided line on the pressure side.

BTW, your low pressure indication could be the vapor lock .... :thumbsup:

As the fuel flashes to vapor it creates a "spring" that the pump "compresses" and "releases" causing the "work" the pump is supposed to do except that it is just compressing the vapor instead of "pumping" the liquid. If you read the pressure of the "spring" it will always be low, thus giving you a false reading.
 

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Discussion Starter #8
Vapor lock is common on these cars. They pick up heat from the engine and cooling system.

I agree with timAT, I would be very carefull about using braided line on the pressure side.

BTW, your low pressure indication could be the vapor lock .... :thumbsup:

As the fuel flashes to vapor it creates a "spring" that the pump "compresses" and "releases" causing the "work" the pump is supposed to do except that it is just compressing the vapor instead of "pumping" the liquid. If you read the pressure of the "spring" it will always be low, thus giving you a false reading.
The line going into the carb is pretty close to the motor and I am going to get a different line from Barry Grant that runs into the carb. I will run the line differently too so I can avoid heating that gas up. My pressure is low even when you first start up the car before it heats up. The fuel pump that is on there probably should not be on the car. I could not even tell you the brand but I know that it is from the early 1980's. I have out a lot of work into this car and there is still a lot more work to do.
 

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I had the exact smae problem with my 76 last weekend. Must have been something in the air in Chicago.............:laughing:

I got the clothespin advice from Rjent and it worked great. It is an awesome temp fix until I find time to re-route the fuel line.
 

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I would NOT use a braided line from pump to carb--TimAT is right, it's still a rubber line, much more susceptible to (catastrophic!!!) failure. Use a steel line and wrap it with insulation. You can buy sleeve or tape type insulation, but if you use tape, put a zip-tie on each end to keep it from coming undone.

(On my small block I have a repro steel line but due to my aftermarket manifold which is about 1" higher, I had to cut it to make it work and now have a 3" section of braided rubber hose just before the carb (Weiand 8000 manifold w/ Q-jet). I have about 2" of steel from the carb, 3" of braided rubber (with maybe 1" gap between the steel sections) and steel the rest of the way from the pump. The steel from the pump to the braided is insulated with tape wrap.)

It does also sound like perhaps you have a fuel pump pressure "issue", those too can be a ladydog to diagnose....and on these cars, to fix. Insulating fuel from heat is probably easiest to deal with first, and can only help performance, so "if I were you" I'd do that first.....

Good luck,
John
 

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Discussion Starter #11
I would NOT use a braided line from pump to carb--TimAT is right, it's still a rubber line, much more susceptible to (catastrophic!!!) failure. Use a steel line and wrap it with insulation. You can buy sleeve or tape type insulation, but if you use tape, put a zip-tie on each end to keep it from coming undone.

(On my small block I have a repro steel line but due to my aftermarket manifold which is about 1" higher, I had to cut it to make it work and now have a 3" section of braided rubber hose just before the carb (Weiand 8000 manifold w/ Q-jet). I have about 2" of steel from the carb, 3" of braided rubber (with maybe 1" gap between the steel sections) and steel the rest of the way from the pump. The steel from the pump to the braided is insulated with tape wrap.)

It does also sound like perhaps you have a fuel pump pressure "issue", those too can be a ladydog to diagnose....and on these cars, to fix. Insulating fuel from heat is probably easiest to deal with first, and can only help performance, so "if I were you" I'd do that first.....

Good luck,
John

Thanks John:partyon:
 

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I picked up some fiberglass and aluminum heat sheath this morning. It is rated to protect up to 500 degrees. I hope it helps because I was having more vapor lock problems.
 

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Something else to think about too, does your car have a fuel return line from the pump or filter to the tank? Part of what it is supposed to do is keep fresh "Cool" fuel circulating between the tank and carb or fuel pump in order to minimize vapor lock. If not equipped for it you may want to concider it as an upgrade
 
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