70 C20 750CFM Quadrajet Fuel Pressure 8psi

[CW4B]

Installing an SMI rebuilt Stage 1 Quadrajet 750CFM carb. I have a new mechanical fuel pump, not sure of the specs but supposedly correct one for year/make/model.

Carburetor instructions insist that fuel pressure should be 5 psi, 5.5 max.

Because I don't have fuel pressure gauge installed normally, I checked fuel pressure by disconnecting fuel line from carburetor and connecting it to a fuel gauge. I then cranked the engine over until fuel gauge showed a stable reading, and that's where I'm getting the 8psi.

Questions:
1) Does this method deliver an accurate reading for this purpose?
2) If no, how should I check fuel pressure?
3) If yes, what can I do to reduce pressue?

Thanks,

[geezer#99]

Tee your gauge into the fuel line and let it idle.
Then see what you get. Could be less. Maybe, maybe not. I’ve seen some read the same.
Quadrajet will run with 8 psi. 5 psi is safer.
You might need a fuel regulator.
Search on summit or jeg’s for one that’s rated up to a max of 6 psi. Get a Holley one.

Congrats on the choice of carb!
SMI has nice carbs.
Last one I bought was 10 bucks!
The guy I got it from thought it was a Holley and didn’t want it.

[CW4B]

Thanks geezer, I will try that out.

[68Gold/white]

It's likely that all stock replacement mechanical fuel pumps are made out of country. I have heard several times of pumps producing too much pressure. 8 psi is too much.

You can either get another pump, or plumb a regulator....not easy, but not impossible either...

Quadrajets are not all created equal. The early models are more pressure sensitive than later models, it depends on the specific carb you have...

ALl; carbs need to be tailored to the soecific engine they are on. hope your deal works out...

[jocko]

What geezer said, get a good gauge reading at the carb inlet.

If it's more than 6 psi, 6.5 psi max, I would be looking at getting a regulator or returning the pump for a different, more well known brand with some history behind it (Holley or Carter mech pump, etc). 8 psi is a bit high, even for a Q-jet. If it were an Edelbrock, you'd probably have some issues already evident.

[CW4B]

Thanks jocko et al, will look for more reputable mechanical pump.

[geezer#99]

Edelbrock has one rated at 6 psi.
Not cheap.
https://www.summitracing.com/int/sea...mps-mechanical