Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: Cadman-iac on June 17, 2025, 09:50:34 AM
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Who makes a decent mechanical fuel pump for a small block Chevy?
I'm currently using a Carter large can pump with a return port on it, and when it gets extremely hot the pressure drops off to almost nothing. It still puts out enough to keep the engine running, but just barely. It puts out up to 9 psi cold, and will maintain around 4 to 5 psi most of the time, but during the heat of the day (100° plus) under a load, such as pulling a trailer and using the air conditioning, the pressure drops to as low as 1-2 psi at idle, but does pick up to about 3 to 3.5 psi at higher RPM's.
I thought about using a pump without a return port, but that would just increase the likelihood of a vapor lock.
I clamped off the return line to see what if any difference it would make and the pressure only increased by 1 psi.
What kind/ brand of pump are you running on your small block, and how well does it handle the heat? Do you have to boost it with an electric pump?
I know I'm operating in extreme conditions, but there must be a pump that can handle the heat, right?
If you are backing up your mechanical pump with an electric pump, what kind are you using, and how well does it do?
The electric pump I'm currently using as a backup is one that looks kinda like a fuel filter with wires, it's a solenoid style. It won't increase the pressure to normal, but does bring it up 1 to 2 psi in this extreme heat.
Rick
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I fought this same demon for years. Engine heat boiling the fuel in the pump. The key
is having sufficient bypass flow to displace the boiling fuel with cooler fuel from the tank.
In answer to your question I don't think there is a high performance 3 port fuel pump.
You may need to use a performance pump, 80-100 GPH and come up with your own
return bypass petween the pump and carb.
Is your existing return to the tank free and unrestricted?
I finally had to revert to an in-tank pump and return line with a bypass regulator
under the hood. No more problems. I really wanted to keep my mechanical pump.
I HATED the idea of an in tank pump. I even passed on a really good deal on
a 880 block because of no fuel pump provision.
QJ
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RobbMC makes a nice mechanical fuel pump. Not cheap though.
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I just googled it. Thats a nice pump AND it has a bypass port.
That may be your ticket Cadman. Had I known about it I may have....hmmmm..
too late now,gone electric.
QJ
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I fought this same demon for years. Engine heat boiling the fuel in the pump. The key
is having sufficient bypass flow to displace the boiling fuel with cooler fuel from the tank.
In answer to your question I don't think there is a high performance 3 port fuel pump.
You may need to use a performance pump, 80-100 GPH and come up with your own
return bypass petween the pump and carb.
Is your existing return to the tank free and unrestricted?
I finally had to revert to an in-tank pump and return line with a bypass regulator
under the hood. No more problems. I really wanted to keep my mechanical pump.
I HATED the idea of an in tank pump. I even passed on a really good deal on
a 880 block because of no fuel pump provision.
QJ
I hate the idea of an electric fuel pump as well, which is just one of the reasons why I removed the original one from the tank.
This used to have a throttle body system on it but wouldn't work with the roller cam, thus the carb and mechanical pump.
So which fuel pump did you finally choose, and what regulator are you using?
There's so many to choose from I honestly don't know where to start, and trial and error can get expensive.
If I have to go back to an in-tank pump though, at least it's already wired for it.
RobbMC makes a nice mechanical fuel pump. Not cheap though.
Yeah, not cheap, but not totally outrageous. My question is how long have these guys been in business? And a 90 day warranty is a bit short for what you're paying. Has anyone here bought and used one of these, what's your experience with it?
Rick
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Looking at this Robbmc website, they're recommending that you use a vented gas cap, but they are assuming you are racing. They also mention using a "cool-can," and wrapping the fuel lines.
A vented cap isn't going to work for a vehicle on the street, your vapor recovery system won't work properly.
Wrapping the lines is impractical, mainly because on a street-driven vehicle the heat build-up would overcome any advantage wrapped lines would give you, that's a quarter mile at a time solution.
And using a cool-can you would have to add ice every 10 miles or less.
So what actual advantage would you have by using one of these pumps if it requires all these other tricks to overcome your low fuel pressure problem for short distances?
I need a solution for long distances in excessive heat. Am I looking for a unicorn?
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My truck is a 92 s10 that was originally a 4.3 v6 with TBI. Now has a near stock
carburated 355 v8. I used a parts store replacement in-tank for the 92 s10.
The regulator is a Holly 12-887 mounted on the AC evap box. The pump outputs
about 12-15 psi and the regulator is set @ 6 1/2 lbs. Also ran new lines while I was at it.
I slid some insulation tubing over the lines under the hood and just behind the engine
although there wasn't any issues with heat, I just did it anyway.
I ran a fuel pressure gauge on the dash for years during the mechanical pump/crappy
gas fiasco. Now there is 6 psi all the time and I finally got rid of the gauge.
There may be better choices for the pump and regulator. Not my area of expertice
but I got lucky and it worked first time. Been about 3 months & 2500 miles, no problems.
QJ
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best thing i did for my Qjet was put an intank pump in my squarebody. the fact you had an electric pump from the get go and removed it is wild.
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That's what I thought when I put an in tank in my Monte.
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RobbMc.
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My truck is a 92 s10 that was originally a 4.3 v6 with TBI. Now has a near stock
carburated 355 v8. I used a parts store replacement in-tank for the 92 s10.
The regulator is a Holly 12-887 mounted on the AC evap box. The pump outputs
about 12-15 psi and the regulator is set @ 6 1/2 lbs. Also ran new lines while I was at it.
I slid some insulation tubing over the lines under the hood and just behind the engine
although there wasn't any issues with heat, I just did it anyway.
I ran a fuel pressure gauge on the dash for years during the mechanical pump/crappy
gas fiasco. Now there is 6 psi all the time and I finally got rid of the gauge.
There may be better choices for the pump and regulator. Not my area of expertice
but I got lucky and it worked first time. Been about 3 months & 2500 miles, no problems.
QJ
I'm ordering a regulator for it today, and gonna put the original pump back in the tank, since the wiring is all there, well mostly anyway. Gotta reconnect the relay to the rear harness again, I rerouted it when I relocated the electric pump to the frame rail.
Let me ask you, what kind of insulation did you use on your fuel lines? How thick was it, and is it split so you can slide it over the lines, or do you have to pull the lines loose from the frame to slide it down the line, and do you think you really got much benefit from it?
Another question, why did you run new fuel lines? Did you increase the diameter, or route it somewhere else to avoid getting too close to the exhaust or something?
I'm hoping by going back to the in-tank pump and installing a regulator that I'll finally stop this heat problem.
I only want to do this once because my hands and knees can't handle much more of it this. I am trying to avoid surgery on both. Getting old sucks!!
Rick
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The insulation I found at SUMMIT. THERMA SHIELD Techflex. Silver foil over white woven fiberglass.
Comes in 4 ft lengths. Split or not split.I used 3/4 and some 1/2 inch. Used it in the engine compartment and down over where it crosses trans bell housing. Used no insulation beyond that.
I prefer it over the DEI 3 ft. short high$ stuff at the parts store.
I ran new lines mostly because the original metal lines toward the front were gone. Fuel injection
grade rubber lines 3/8 supply from pump output to regulator, 1/4 inch new line from the regulator
to a return line fitting plumbed into the top of the fuel pump. The 5/16 inch original return line
is now an emergency get me home fuel supply using a holly mighty mite inline pump. Should
the in tank pump fail I can swap one wire and one hose under the hood and be on my way.
I get the part about knees back and aches & pains. I don't own a lift, just a set of ramps and a
couple of jacks.
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Also the insulation I used is not very thick at all. And you wont need it except maybe under the hood
and near exhaust parts. Lines on the frame rail shouldnt be much of a problem.
The circulation of fuel and the fact that its no longer under a vacuum accounts for much of
the magic that goes with in tank systems.
QJ
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make sure to retain the oil switch in the fuel pump circuit. it is usually just above the oil filter on the TBI trucks, but you can use the oil gallery under the distributor as well. this serves 2 purposes, 1. if your relay dies, once you crank enough to get above 5 psi, the pump will energize from the oil switch alone 2. takes load off the relay contacts for longer contact life.
also don't use regular fuel line in the tank,.you need to get fuel hose rated submersible. usually black hose with a pink stripe on it.
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Also the insulation I used is not very thick at all. And you wont need it except maybe under the hood
and near exhaust parts. Lines on the frame rail shouldnt be much of a problem.
The circulation of fuel and the fact that its no longer under a vacuum accounts for much of
the magic that goes with in tank systems.
QJ
Thanks QJ, I couldn't get the Holley 12-887, it's backordered according to Holley, but they suggested using a 12-803BP if I didn't need the gage port and didn't care if it was chrome instead of black.
Besides the almost double the cost price tag, I asked if it was made in China, "OH no!! Definitely not" they said.
So I called Summit and ordered it. It showed up today, made in Thailand!! Another call to Summit and it's on its way back to them.
Supposedly the Edelbrock EDL-1789 is American made, so I was told anyway, so it should be here by Wednesday.
You are right, an in-tank pump will end this heat issue. I still have the new pump I bought for the TBI system, I'll put it back in once I have an American made regulator in my hands.
Thanks for your help with this I appreciate it.
Rick
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make sure to retain the oil switch in the fuel pump circuit. it is usually just above the oil filter on the TBI trucks, but you can use the oil gallery under the distributor as well. this serves 2 purposes, 1. if your relay dies, once you crank enough to get above 5 psi, the pump will energize from the oil switch alone 2. takes load off the relay contacts for longer contact life.
also don't use regular fuel line in the tank,.you need to get fuel hose rated submersible. usually black hose with a pink stripe on it.
Tayto,
I lobotomized the computer once I decided to go with the carburetor. I removed the check engine light and replaced it with a choke indicator light.
Unfortunately I couldn't make the pump relay work in conjunction with the choke and light. The electric choke coil would draw too much of the current that the relay would not energize.
Not sure why it didn't work, but I gave up trying and just wired the relay through a switch under the dash instead.
Would you know how to get the factory pump relay to work through the oil pressure switch and also energize the electric choke and the indicator light?
The only way I can see to do both is to use 2 different oil switches. Any suggestions?
Rick
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Good luck finding a quality American product for cheap.
For cheap you get a Chinese product no matter what it says on the box.
And yes, the box may be made in the USA but the contents may not.
FWIW
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These guys seems to have quality products:
https://www.magnafuel.com/carbureted-regulators.html
https://robbmcperformance.com/products/regulator_bp.html
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Why couldn't you just use a Carter M4891 style mechanical pump with a Jeep Wagoneer fuel filter, which has a built in return line port? I never liked the idea of putting an electric fuel pump in the gas tank for a number of reasons, and external electric pumps have problems of their own, such as being able to put them in the best location and wiring them properly so they are safe.
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Cadman, check out revolution electronics fuel pump controller 12003.
Available from the mfg. or several other online sites. Made in USA.
about 75$. Doesn't need oil pressure logic, works from tach signal.
I have one but have never got around to installing it yet. Gonna
have to put it on the DO list.
QJ
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What does a choke indicator light do....????
I used the original key-on wire for the v6 distributor to power up the v8 HEI distributor,
electric choke and at times a fast idle solenoid. plenty of voltage for all 3.
Fuel pump is another circuit that goes through the oil pressure switch. There is no automatic
prime. I have a button on the dash for that.
Should take very little current to power a relay and choke heater....
QJ
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I'm fairly sure GM had a 3 wire switch that would do the fuel pump and oil pressure light (choke light). I will have to search. In my square body I actually have the TBI running everything but the injection. sure is nice to change timing with a couple key strokes and then flash it to the ECM
EDIT: i think this is the correct sender:
https://www.rockauto.com/en/moreinfo.php?pk=44300&cc=1143964&pt=4588
my experience has been they all use the same plug but only use 2 pins instead of 1, so should be easy enough to add the extra wire.
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I figured out why I couldn't get the fuel pump relay to work with the electric choke through the oil pressure switch. I was trying to use the switch to ground the relay in the same way that the ECM did for the TBI system by controlling the relay ground. I need to use the oil switch to break the power from the relay to the pump instead.
QJ, you mentioned that you put your regulator on your evaporator case, what was the reason for this location?
Did you use the original fuel lines that ran up the transmission to the back of the engine, or did you reroute them?
Did you use any hose? I've been looking at getting some stainless steel braided fuel hose to go between the regulator and the carburetor. I was thinking about cutting out the original braided hose for the TBI to use for this, but I don't know if this original hose will be in good enough condition.
Also, the Edelbrock regulator that Summit Racing had recommended didn’t have a return port, so I sent it back and ordered an Aeromotive regulator. I'm much happier with this one, it's American made, but it is also adjustable from 3-60 PSI by changing the spring.
I believe I will move the fuel lines from the inside of the frame rail to outside the frame to keep it cooler. I can bring it up from underneath the evaporator case and locate the regulator in front of it. What do you think?
Rick