General Category > Quadrajet Carb Talk and Tips
Quality, reliable mechanical fuel pumps
Cadman-iac:
Well I got it installed on the firewall to the passenger side of the distributor, and i got the original fuel lines reinstalled and modified to fit the carb and the regulator.
I kept trying to find a way to keep the mechanical pump as a backup for the inevitable failure of this magnificent Chinese electric pump in the tank, but the logistics were too difficult.
I did however keep the electric pump on the frame rail. I tested the tank pump and it pumps right through the rail pump without any issues, and I tested the rail pump to see how well it would draw through the tank pump and it works great. The two work perfectly and will put out enough pressure to keep the carburetor happy.
As for the cutoff, I wired through the oil pressure switch, and instead of buying that Revolution Electronics fuel pump controller 12003 to prime it when you turn on the key, i found out that I can use the original pump priming module, GM calls it a "Hot Fuel Handling Module ", which does not need to go through the ECM. It's just got 3 wires, a ground, a hot from the ignition switch, and the output to the pump which is tied into the same wire coming from the original fuel pump relay. Turn the key on and i get 20 seconds of power to prime the system.
I did a little research on these because I have 2 square body Suburbans, a half ton and a 3/4 ton. The heavier vehicles were outfitted with the longer running module, the light duty ones got a 3 to 4 second module, which i confirmed on mine.
I just got the wire harness back into the truck last night and did some preliminary tests to make sure I got everything wired correctly. I'll take it out today and make sure there's no problem on the road. So far though I'm very happy with it.
One thing that I've noticed since installing the regulator is the AFR is more steady at an idle. The fluctuations are very minimal now.
Cadman-iac:
Here's a couple of pictures of how I plumbed the fuel lines and regulator. I finally figured out how to post pictures.
The original fuel lines reinstalled and modified to fit the carb and the regulator is mounted on the firewall above the supply and return lines.
I made a "manifold" or i guess it's more like a "fuel rail" out of a "tee" fitting and 3 pipe to inverted flare 90° fittings.
Now the only portion of the line that doesn't have constantly circulating fuel in it is just the short section between the tee and the carb. This will prevent any issues with heat soaking and vapor lock.
With the factory "Hot Fuel Handling Module " running the pump for 20 seconds each time the key is turned on, I should always have a full carburetor bowl.
quadrajam:
That looks really good. Now you will have plenty of fuel all the way to the end
of the 1320.
A few months from now you will be going "mechanical WHAT " .
QJ
Cadman-iac:
--- Quote from: quadrajam on September 19, 2025, 05:02:53 PM ---That looks really good. Now you will have plenty of fuel all the way to the end
of the 1320.
A few months from now you will be going "mechanical WHAT " .
QJ
--- End quote ---
If I try getting to the end of a1320 foot run in a timely manner, I'll need stock in an oil company, lol! This is a HEAVY truck.
That said, I made a run to Tucson and back today and checked the mileage, it got 11.73 miles per gallon at speed with the a/c on during the return, which is the uphill run.
I think I have more work to do to fine tune it, but watching the AFR gage on the run, at 70mph and at 3000 rpm with a vacuum reading of 10", the AFR was fluctuating between 14.0:1 to 15.3:1.
I noticed the AFR at idle was running around 11.2:1, so I leaned the idle mixture slightly and brought it up to around 12.9:1. Doing this seems to have an effect on the AFR at higher RPM's, is that normal?
At what point does the idle circuit cease to have an effect on the main circuit?
tayto:
11:1 to 12:1 is WOT mixture territory. should be in the 13.5:1 to 14:1 for idle.
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