[Formulabruce]

STOCK Fuel pump for a friends 8.3:1 Pontiac 400. ( can size doesn't matter, its a driver)
The stock pump bypasses excess pressure to the return line to tank, leaving 4-5 psi to the Q jet.
To replace the pump with a pusher ele. Pump outside the tank rated at 4-7 psi would eliminate the carb bowl evap issues. I have done this and left the factory pump in place and only had a 5 second limit on the electric. Worked fine.
Question.. If a fuel pressure regulator adjustable from 4-7 psi Took the Place of the factory pump, and the electric pump left ON with key, will the SECOND output of the regulator ( has one in and Two out) act same as stock mechanical pump as a return line?
CARB engine, LOW fuel pressure..
Anyone tried this on a stock style engine?

[tom s]

I did once early on my 63 tempest.Blew a fuse about 1/2 mile from my house.Carter Street pump went on.Tom

[tom s]

Still have the pusher on a switch for priming and racing.Tom

[25stevem]

I had a pusher for a while feeding the stock pump and one time the pusher did crap out, yet the stock one was able to suck enough fuel thru it to let me limp home.
This was with a vane type electric pump.

[78w72]

Originally Posted by Formulabruce

STOCK Fuel pump for a friends 8.3:1 Pontiac 400. ( can size doesn't matter, its a driver)
The stock pump bypasses excess pressure to the return line to tank, leaving 4-5 psi to the Q jet.
To replace the pump with a pusher ele. Pump outside the tank rated at 4-7 psi would eliminate the carb bowl evap issues. I have done this and left the factory pump in place and only had a 5 second limit on the electric. Worked fine.
Question.. If a fuel pressure regulator adjustable from 4-7 psi Took the Place of the factory pump, and the electric pump left ON with key, will the SECOND output of the regulator ( has one in and Two out) act same as stock mechanical pump as a return line?
CARB engine, LOW fuel pressure..
Anyone tried this on a stock style engine?

to answer your question about a return style regulator acting as stock return, i dont think its the same. the stock return is only a vapor return, very little fuel flow is returned to the tank.

a return style regulator is a full flow return to the tank & from what ive read & been told its not a good idea to run a full return regulator on a mechanical pump, lowers the psi too much & a stock pump probably cant keep up with that full return flow.

if you want to use a pusher pump for easy starts after the car has sat a week or more, get an electric pump that allows fuel flow when its off or make one of the bypass set ups thats been posted on here a few times. i think one of the models of carter elect pumps allow full flow when turned off, then can turn on for starts or when need more fuel flow.

[Singleton]

It sounds like you're asking if a non-return regulator can be used as a return, (bypass), regulator by sending one output to carb and one back to the tank? I would think that all the fuel would follow the path of least resistance and go to the tank leaving no pressure to the carb.

Better idea is to use an actual bypass regulator to precisely set the fuel pressure to the carb and send the excess back to the tank as designed. I use this setup with a mechanical pump on my own car. I set the pressure to 6psi and send a small amount back to tank just to keep the fuel moving in the lines at all times to avoid boiling

[78w72]

Originally Posted by Singleton

It sounds like you're asking if a non-return regulator can be used as a return, (bypass), regulator by sending one output to carb and one back to the tank? I would think that all the fuel would follow the path of least resistance and go to the tank leaving no pressure to the carb.

Better idea is to use an actual bypass regulator to precisely set the fuel pressure to the carb and send the excess back to the tank as designed. I use this setup with a mechanical pump on my own car. I set the pressure to 6psi and send a small amount back to tank just to keep the fuel moving in the lines at all times to avoid boiling

wasnt sure if he meant a true return reg or a dead head one just using the 2nd output option... if its a dead head & you try & use the 2nd outlet, then i agree 100% that the fuel will take the path of least resistance, deadhead reg's arent designed to use the other outlet as a return.

a return regulators internal diaphragm allows it to function to where only the non used fuel gets returned & the main outlet gets the adjusted psi fuel flow. but again, thats not usually recommended on a mechanical pump, it may work for some applications with a higher flow mech pump, but a stock one probably wont hold proper psi using a return regulator. robbmc told me not to use a return reg with their pumps, they are designed to run deadheaded or use their vapor return set up that has a very small .040 metered hole.

if the main concern is to use an electric pump to fill the bowl after fuel evaporates, just buy one of the pump types that allow free flow when not in use or make up the bypass assembly of hardware store fittings thats been posted here, i think tom v posted about them awhile back.

[Singleton]

I’ve been using a bypass regulator with the RobbMc 550 mechanical pump for about 5 years with success. Plugged the return on the pump body, and have the regulator after the carb sending a small amount back to tank. I set it at 5-6 psi, so the flow going back to tank isn’t much but keeps fuel moving.

[78w72]

i dont doubt its working for you, just saying its not recommended & is limiting the flow/psi capability of the pump, although that apparently doesnt matter for your engine/fuel needs.

also being your regulator is after the carb, that may be functioning differently than the standard location for a regulator that is in front of the carb, that is what robbmc & most others say not to do.

for the Op the simple answer is a elect pump that allows free flow or making up the bypass fittings.

[Tom Vaught]

I made up a custom Fuel Supply one time for a guy who was running one of the POS Mechanical Fuel Pumps from China that would have normal fuel pressure of 9-10 psi vs the old stock stuff which ran at 5.5 to 6 psi fuel pressure, (no regulator required for old stuff).

So the carb was a Holley Carb and the Fuel Pump would send the fuel to the Holley fuel lines/ bowls, but the rear of the new carb fuel line had a connection to a Holley By-pass Fuel Pressure Regulator. The one used on the low pressure by-pass systems. 12-881 is the new number, it used to the the "red" low pressure regulator years ago. Red Regulator = < $50, new stuff is $150 from Summit/Jegs.

The Carb Fuel Line looked like this. I cut the line before it curved to the rear fuel bowl and installed a 'tee" there and connected the "tee" to the by-pass regulator. The By-pass Regulator outlet returned the fuel to the tank with a extra frame fuel line. Chebby Guy.

Worked well with the Chinese crap and was cheap compared to the $150 (same) regulator sold today. Pic is of new stuff.

Tom V.

[78w72]

heres the bypass fittings i was talking about that tom v posted some years back. but last i knew carter does make a lower cost low psi elect pump that allows free flow when not in use, just cant remember which specific one...

https://forums.maxperformanceinc.com...94#post5573494

[zippy]

I run a Holley Blue at my tank, with a deadhead style reg under the hood. Been working great on my 455. I do want to upgrade to a return style eventually, as the Blue is kinda noisy.

[Tom Vaught]

Blue is Noisy AND has contamination issues where if you do not have a proper fuel screen on the tank pick-up the vanes will get stuck in a leakage position and the fuel pump will not perform to advertised conditions.

Tom V.

[zippy]

Originally Posted by Tom Vaught

Blue is Noisy AND has contamination issues where if you do not have a proper fuel screen on the tank pick-up the vanes will get stuck in a leakage position and the fuel pump will not perform to advertised conditions.

Tom V.

Good to know, Thx.

[Shiny]

Originally Posted by Tom Vaught

I made up a custom Fuel Supply one time for a guy who was running one of the POS Mechanical Fuel Pumps from China that would have normal fuel pressure of 9-10 psi vs the old stock stuff which ran at 5.5 to 6 psi fuel pressure, (no regulator required for old stuff).....

I suspect this "high pressure" from a cheap pump was a contributor to a flooding issue I had when I last tried to get my car running.

Is there a brand of mechanical pump I can buy with known low pressure? It's a 70 LeMans with a 1/4" return line.

Originally Posted by 78w72

...

if you want to use a pusher pump for easy starts after the car has sat a week or more, get an electric pump that allows fuel flow when its off or make one of the bypass set ups thats been posted on here a few times. i think one of the models of carter elect pumps allow full flow when turned off, then can turn on for starts or when need more fuel flow.

...last i knew carter does make a lower cost low psi elect pump that allows free flow when not in use, just cant remember which specific one...

Can anyone point me to a discussion/recommendation for a specific low-pressure "pusher" pump that I can use to fill the carb after it sat for a while? Does Carter make one as described here?

[78w72]

not sure how low of psi you need with that carb, but for a performance option the carter or edelbrock pumps are set at ~6psi. they are deadhead with no vapor return but that has never been an issue on for me when using that style of pump, using a robbmc now with no vapor line or full return regulator, runs great in all conditions/heat. no vapor lock or other issues some seem to have.

maybe the factory pump you had was defective putting out too much psi, ive heard about that before on aftermarket stock pumps. maybe try another one from a different brand, most parts stores will allow a return if its defective.

as for the carter pump, sorry i dont recall the specific model # but i know a lot of guys have used them & mentioned it here in past years, hopefully one can comment on that... or just call carter tech line & ask which one allows fuel flow when off? one certain type of pump allows that, maybe its the rotary vane type like this carter? or go to the hardware store & make the bypass set up tom v posted & use whatever electric pump you want.

https://www.summitracing.com/parts/crt-p4070?rrec=true

[Shiny]

78w72 - Thanks for the quick response

I will investigate the Carter "pusher" pump.

As to my mechanical pump, it's been ~15 yrs since I installed it and I don't remember what it was. I just know I had a flooding issue and suspected the pump as I also understood some aftermarket pumps were known to put out higher pressure.

Mike

[78w72]

Originally Posted by Shiny

78w72 - Thanks for the quick response

I will investigate the Carter "pusher" pump.

As to my mechanical pump, it's been ~15 yrs since I installed it and I don't remember what it was. I just know I had a flooding issue and suspected the pump as I also understood some aftermarket pumps were known to put out higher pressure.

Mike

the issues with aftermarket pumps seems to have been fairly recent, like ~10 years, but any china made cheap pump can have issues. a 15 year old one if in good working shape should or could be putting out correct psi. need to put a gauge on it to verify that though.

the edlebrock pump i had was dead on at 6psi & supported 520hp on the dyno, at the track it showed pretty bad starvation below about mid to low 12's... the robbmc supports low 11's, but on hard launches with good traction it has issues too. intank electric is in my future if i want to go any faster.

check for others issues that could cause flooding, improper adjusted float, bad float or needle/seat etc. a gauge will show if the pump has too much psi.

[Shiny]

Thanks again.

I'm going to go out and see what pump I have.

If anyone has a KNOWN source for a mechanical pump that puts out 4 to 6 psi, please chime in.

It's a stock 70 350, quadrajet added, so I don't need a "performance" pump...just one that works without over-pressuring the carb inlet.

Here's a thread discussing excess pump pressure but unfortunately, there was no real conclusion about what pump does what. There are several mentions of 10psi:

"http://forums.maxperformanceinc.com/forums/showthread.php?t=811240&highlight=pressure"

In that thread, I shared a video of my pump pressure while just cranking. I thought it was too high but without the engine running, was hard to interpret:

https://1drv.ms/v/s!AiIRc33Ia4jVg-g6...LFSkA?e=Pmj2BK

Before chasing the pump pressure, I had verified the carb inlet was capable of seating which led to discovering a rust mess. I installed a filter to get by for the moment but never resolved the cause of the flooding. After sitting for ~3 yrs, I'm now going after the rust and thought I'd revisit the pump pressure hypothesis while I've got the tank out.

Mission creep.... but that's where I am.

[Shiny]

Here's my pump. I don't see a brand so probably a generic short-can.

The filter was my band-aid to try and get the car running in spite of rust.