How much will carb size affect fuel pressure needs?

[wpwarren]

I am chasing down an intermittent stalling problem and I have a carb question. I have worked on cars, but never anything that wasn't fuel injected until the last couple of years so I still have a lot to learn. I have a 73 blazer with a 74 454 swapped into it. It has an edelbrock performer 750 cfm carb on it which was rebuilt last summer. The fuel pressure specs I can find online say 8-10 psi for the stock carb setup. I am running 8 or just over 8 psi after the fuel filter. I know I have spark problems so that is something I am fixing first, but will my fuel pressure be causing me issues too?

 

[ChrisPerry]

5-6 psi on all but the highest performance race engines. If you are running 8+ psi the carb will have flooding issues. If you have an adjustable pressure regulator dial it down to 5psi and see if that helps.

 

[wpwarren]

5-6 psi on all but the highest performance race engines. If you are running 8+ psi the carb will have flooding issues. If you have an adjustable pressure regulator dial it down to 5psi and see if that helps.

is that true for a big block? My chilton manual says 8-10 psi for a 74 454. And unfortunately no regulator.

 

[ChrisPerry]

is that true for a big block? My chilton manual says 8-10 psi for a 74 454. And unfortunately no regulator.

I'm not sure about the stock carb, but all Edelbrock and Holley carbs are 5-6psi at idle. 8psi+ will cause stalling under braking and when quickly changing directions at low engine RPMs. If you are still having stalling issues (fuel related) after lowering the fuel pressure, you should check the float level. Go to Edelbrocks trouble shooting guide to see how to properly set the float level. It's pretty easy to do.

To properly adjust the floats in the EPS carburetor, two procedures must be followed. First, invert the airhorn cover holding the airhorn gasket in place. There should be 7⁄16"
between the airhorn gasket and the top of the outer end of the float. To adjust the float level, bend the float lever until the recommended level is attained. DO NOT press the needle into the
seat when adjusting the float lever. Next, you should check the float drop. Hold the airhorn upright and let the floats hang down. There should be 15/16" to 1" between the
airhorn gasket and the top of the outer end of the float. To adjust the float drop, bend the tab on the back until the recommended float drop is attained.

Off-Road
Although the Edelbrock Performer Series carburetor was not calibrated with hill climbing and other extreme off-road operation in mind, it can be made to perform superbly by substituting
Edelbrock #1465 spring loaded needle and seat for the original needle and seat. The spring loaded needle and seat act like a shock absorber, reducing the possibility of flooding during
off-road operation. After installation of the new needle and seat you must reset the float level to 7/16" and drop the float drop to 15/16 to 1" as outlined in “FLOAT ADJUSTMENT”.

 

[K85 Octane]

I'm not sure about the stock carb, but all Edelbrock and Holley carbs are 5-6psi at idle. 8psi+ will cause stalling under braking and when quickly changing directions at low engine RPMs.

Yep, your PSI should match your carb, not the truck. 8 psi is probably overpowering your fuel valve spring and causing some flooding issues, like already explained. Unless it's a beast of a motor running high rpm all the time, 5-6 psi is good. My families boat runs 6 psi, 427 bbc, and you know rpms are turning.

Fix your ignition thing and maybe switch out your fuel pump, or get a regulator for it.

 

[wpwarren]

good info! Thanks guys. I will have time to mess with it in a few days.

 

[wpwarren]

So after lots of fidgeting and testing and trying things I ended up buying an inline pressure regulator and am getting 6 psi to the carb now and it seems happy. That combined with new cap, rotor, plugs, plug wires, and uni-lite control module and the blazer is happy again.