Carb Fuel pressure help

[Andy]

I just recently installed a summit liquid filled in line fuel gauge and have notice a low fuel pressure after driving around town. When I first start the car at idle it reads 6.5-7 psi perfect for carbs. Then I drove it and pulled over to check things and noticed the fuel pressure was reading 2.5 to 3 psi. I have a 600cfm holley with vacuum secondaries, stock fuel pump, I jetted it up to number 70 jets. It seems to be heat related. I have the old efi filter in line as well as one of those glass in line fuel filters. The efi fuel filter that is near the tank is about 3years old. I wouldn't think it is filter related since it has normal pressure on start up. Also I have mostly rubber fuel lines in the engine bay and have covered them with a heat jacket thats supose to protect against heat up to 500F. Parts of the fuel line are near the block but are not touching. The car seems to be running fine, but was worried it would be running lean because of the low fuel pressure.
Any ideas? One other thing I shut the car off for about 5 minutes and left the fan on and then started it up again and the pressure was reading 4 to 4.5 psi:confused:

Any help would greatly be appreciated.

[mustangrfast88]

what kind of fuel pump are you running

[Andy]

Oh, its a stock mechanical. And I don't know how old it is. I am starting to think that it maybe my problem. I think it may be getting heat socked. I was hoping someone had a similar problem. I was thinking about buying one of those low pressure inline electric fuel pumps.

[mustangrfast88]

so the pump is in the tank or on the side of the motor and if it is the stock in tank pump you shouldnt try to run a efi pump on a carb car inless you are running a return line. the regulator trys to bring the pressure down to much and that makes the pump overheat. you need a holley blue fuel pump

[Andy]

so the pump is in the tank or on the side of the motor and if it is the stock in tank pump you shouldnt try to run a efi pump on a carb car inless you are running a return line. the regulator trys to bring the pressure down to much and that makes the pump overheat. you need a holley blue fuel pump

Nope the stock efi in tank electric pump was removed during the swap. I have a Mechanical pump that bolts to the side of the motor. No regulator present. The mechanical pump does use the return line.

[mustangrfast88]

i would run some new lines and get a block off plate and get you a electric fuel pump the holley blue is what i run with there regulator.

[Mista Bone]

I don't think the mechanical pump on the block can "suck" the fuel well enough thru the EFI filter.

As a test, pull the EFI filter out and use a short section of rubber fuel line, make a test drive........if pressure stays up PROPERLY hard line where the filter was.....no need for another fireball.

[mustangoutlaw]

I just recently installed a summit liquid filled in line fuel gauge and have notice a low fuel pressure after driving around town. When I first start the car at idle it reads 6.5-7 psi perfect for carbs. Then I drove it and pulled over to check things and noticed the fuel pressure was reading 2.5 to 3 psi. I have a 600cfm holley with vacuum secondaries, stock fuel pump, I jetted it up to number 70 jets. It seems to be heat related. I have the old efi filter in line as well as one of those glass in line fuel filters. The efi fuel filter that is near the tank is about 3years old. I wouldn't think it is filter related since it has normal pressure on start up. Also I have mostly rubber fuel lines in the engine bay and have covered them with a heat jacket thats supose to protect against heat up to 500F. Parts of the fuel line are near the block but are not touching. The car seems to be running fine, but was worried it would be running lean because of the low fuel pressure.
Any ideas? One other thing I shut the car off for about 5 minutes and left the fan on and then started it up again and the pressure was reading 4 to 4.5 psi:confused:

Any help would greatly be appreciated.

Try checking it with another gauge that is not liquid filled! I had the same problem on a car and it turn out to be the liquid filled gauge! liquid filled gauges and heat don't mix well with carbs because they need to be very accurate (i.e. 6 1/2 or 7 psi) the liquid heats up and makes the gauge read wrong and cools and you have another reading that is different! this was the case on my car! I drained the liquid out and the gauge works great now! I don't know if it will work for you but it is something to check! my .02 worth

[Andy]

Try checking it with another gauge that is not liquid filled! I had the same problem on a car and it turn out to be the liquid filled gauge! liquid filled gauges and heat don't mix well with carbs because they need to be very accurate (i.e. 6 1/2 or 7 psi) the liquid heats up and makes the gauge read wrong and cools and you have another reading that is different! this was the case on my car! I drained the liquid out and the gauge works great now! I don't know if it will work for you but it is something to check! my .02 worth

Did your gauge bounce back and fourth alot. Mine jumps around some until I bring the idle up and then it steadies out. Did yours do that or was it smooth the whole time. I did try a non liquid filled gauge, it was from cheapy one from pep boys. When the pep boys one was installed I could never get a reading no matter what rpm i held the engine, the needle jump like crazy. I thought is junk and took it back.

I will eliminate the efi filter in the back, maybe that is causing the issue.

[mustangoutlaw]

Mine would jump around for a min. or 2 then be steady but each time I would start it after it got warm, it would be a diff. reading!

[Andy]

Okay, I bypassed the efi fuel filter with a rubber hose and test drove it. It didn't seem to make a difference on the pressure, but I think i will leave it off cause it has to be restrictive. Anyhow it was reading 3psi, so i took a can of freeze spray and sprayed it on the gauge and the readings started to raise back up to like 5.5 to 6:confused: So maybe it is the liquid in the gauge or just the guage in general. I was hoping that the gauge was setup to handle this type of application. So I think my pressure is okay, I just may try and drain the liquid out and see what happens. Thanks for all the help:bigthumb

[mustangoutlaw]

Okay, I bypassed the efi fuel filter with a rubber hose and test drove it. It didn't seem to make a difference on the pressure, but I think i will leave it off cause it has to be restrictive. Anyhow it was reading 3psi, so i took a can of freeze spray and sprayed it on the gauge and the readings started to raise back up to like 5.5 to 6:confused: So maybe it is the liquid in the gauge or just the guage in general. I was hoping that the gauge was setup to handle this type of application. So I think my pressure is okay, I just may try and drain the liquid out and see what happens. Thanks for all the help:bigthumb

:cool1: Let me know what happens.