Pontiac GTO Forum banner
1 - 20 of 31 Posts

·
Registered
Joined
·
109 Posts
Discussion Starter · #1 ·
I haven't checked it yet, but I suspect my auto parts store, mechanical ,fuel pump is putting out too much pressure. What brand of stock pump are you using on your Pontiac?
 

·
Registered
Joined
·
80 Posts
I bought one from Ames and ended up with same issue too much pressure. Maybe not the solution you want but put a fuel pressure regulator on it and it fixed the issue
 

·
Registered
Joined
·
109 Posts
Discussion Starter · #3 ·
I was hoping to avoid a regulator, but with the lack of quality in replacement parts, it looks like my next step.
 

·
Registered
Joined
·
895 Posts
I was hoping to avoid a regulator, but with the lack of quality in replacement parts, it looks like my next step.
Carter fuel pumps. Doubtful they have to much pressure....might be a carb/float issue
 

·
Registered
1967 400/400
Joined
·
2,115 Posts
Myself and a few of the other people here (I think Bear and Lemans Guy?), run the Edelbrock. It's clockable and put's out exactly 6psi (depending on the model you get). Plus it's just a rebuildable, pro pump, which has greater volume capacity and it rebuildable.
 

·
Registered
Joined
·
80 Posts
I was hoping to avoid a regulator, but with the lack of quality in replacement parts, it looks like my next step.
Certainly make sure any potential needle seat or float issues are resolved first.

If you have a rebuildable pump these guys have been mentioned in the past as getting them set up for a stock pressure. Then and Now Automotive

The Ames one I put on was doing 6-7 psi which would flood my Tripower set up and cause AFR wandering at idle. I have it set 3.4-4 psi and works great now.

If you do go with a regulator be careful with gauge selection - i used a inexpensive Summit gauge on a Holley 12-804 ( 4 psi regulator), the liquid filled summit gauge gives variable pressure indication depending on gauge temp... so I put it on adjusted it to 4 came back was reading low... adjusted it up ... and had the same flooding issues - tried different needle and seats... and realized with that liquid fill gauge I had to set it when cold then ignore it.

Once I did that the set up works great and I get good AFR across the rpm and throttle position range.
 

·
Registered
Joined
·
109 Posts
Discussion Starter · #7 ·
When I bought the car it had a Holley carb that was running rich, just like the factory Q jet is now, I just had the Q jet rebuilt by a pro shop, so going to check the pump pressure before I look at the carb. I'll test the Carter pump soon and post results. The car had a cheap liquid filled gauge that showed erratic psi readings, if I need a gauge and regulator, I'll buy an Aeromtotive brand, I had good luck in the past with them.
 

·
Registered
Joined
·
6,005 Posts
When I bought the car it had a Holley carb that was running rich, just like the factory Q jet is now, I just had the Q jet rebuilt by a pro shop, so going to check the pump pressure before I look at the carb. I'll test the Carter pump soon and post results. The car had a cheap liquid filled gauge that showed erratic psi readings, if I need a gauge and regulator, I'll buy an Aeromtotive brand, I had good luck in the past with them.
As has been mentioned here before, maybe you read it? The liquid filled gauges can fluctuate due to the internal pressures within the gauge itself. I recall someone saying they drilled a relief hole in the housing and that cured the fluctuations. (y)
 

·
Registered
1967 400/400
Joined
·
2,115 Posts
As has been mentioned here before, maybe you read it? The liquid filled gauges can fluctuate due to the internal pressures within the gauge itself. I recall someone saying they drilled a relief hole in the housing and that cured the fluctuations. (y)
This is why I always recoment the Marshall guage to everyone. Theyve been in the game forever, are cheap, American made, have tech support, and a relief valve built in.
 

·
Registered
Joined
·
109 Posts
Discussion Starter · #11 ·
Thanks, I'll check out the Edel pump and Marshall gauge, here's some info from Aeromotive.
uid-Filled Gauges vs. Dry Gauges, The Problem and the Solution – TB #903

Click here to download the pdf.

Finding a fuel pressure gauge that is accurate, reliable, and affordable proves to be a surprisingly difficult job – more so than most enthusiasts realize. There are two main types of gauges on the market: liquid-filled gauges and dry gauges. A liquid-filled gauge is tougher and more durable than a dry gauge. If a dry gauge is under extended shock and vibration, its internals can get damaged and the needle falls off. The oil in a liquid-filled gauge protects its precision internals from shock and vibration, solving this issue. And there’s no arguing that a liquid-filled gauge looks like a higher quality instrument.

Unfortunately, there’s a hidden “gotcha” that users of this type of gauge experience: a reported lack of accuracy and consistency is common. In fact liquid-filled fuel pressure gauges do exhibit seemingly random pressure swings. The reason this happens is because, as the temperature under the hood heats up, the oil in the gauge heats and expands, causing the needle to move without any kind of pressure change within the system. Dry gauges, on the other hand, do not have these pressure swings that liquid-filled gauges do.

Here at Aeromotive, we are focused on eliminating fuel system compromises wherever possible, including gauge inconsistency. Our new liquid-filled gauges feature a special sealing plug that is fitted with a stainless steel pin-valve that can be pulled up slightly to equalize internal pressure and then pressed back down to re-seal. The gauge remains sealed but able to be equalized at any time, regardless of gauge temperature, immediately restoring accuracy and eliminating heat-related inconsistency.

Note: in order to use the pin-valve effectively, these new gauges require mounting so the face of the gauge is perpendicular (at a right angle to) the ground, and with the pin-valve/plug assembly on top.

Designed to the smaller, 2″ diameter size most popular with enthusiasts across the motorsports spectrum, these exciting new gauges feature a stainless steel case, polished bezel, heavy-duty brass 1/8″ NPT male connector, and are compatible with 1/8″ NPT female pressure ports found in most performance fuel pressure regulators. The white face with black numbers and hash marks is easy to read and includes the Aeromotive name and logo. Two versions are currently offered; 0-15 PSI P/N 15632 and 0-100 PSI P/N 15633, and are available now through any Aeromotive dealer or at: www.aeromotiveinc.com.
 

·
Registered
1967 400/400
Joined
·
2,115 Posts
Thanks, I'll check out the Edel pump and Marshall gauge, here's some info from Aeromotive.
uid-Filled Gauges vs. Dry Gauges, The Problem and the Solution – TB #903

Click here to download the pdf.

Finding a fuel pressure gauge that is accurate, reliable, and affordable proves to be a surprisingly difficult job – more so than most enthusiasts realize. There are two main types of gauges on the market: liquid-filled gauges and dry gauges. A liquid-filled gauge is tougher and more durable than a dry gauge. If a dry gauge is under extended shock and vibration, its internals can get damaged and the needle falls off. The oil in a liquid-filled gauge protects its precision internals from shock and vibration, solving this issue. And there’s no arguing that a liquid-filled gauge looks like a higher quality instrument.

Unfortunately, there’s a hidden “gotcha” that users of this type of gauge experience: a reported lack of accuracy and consistency is common. In fact liquid-filled fuel pressure gauges do exhibit seemingly random pressure swings. The reason this happens is because, as the temperature under the hood heats up, the oil in the gauge heats and expands, causing the needle to move without any kind of pressure change within the system. Dry gauges, on the other hand, do not have these pressure swings that liquid-filled gauges do.

Here at Aeromotive, we are focused on eliminating fuel system compromises wherever possible, including gauge inconsistency. Our new liquid-filled gauges feature a special sealing plug that is fitted with a stainless steel pin-valve that can be pulled up slightly to equalize internal pressure and then pressed back down to re-seal. The gauge remains sealed but able to be equalized at any time, regardless of gauge temperature, immediately restoring accuracy and eliminating heat-related inconsistency.

Note: in order to use the pin-valve effectively, these new gauges require mounting so the face of the gauge is perpendicular (at a right angle to) the ground, and with the pin-valve/plug assembly on top.

Designed to the smaller, 2″ diameter size most popular with enthusiasts across the motorsports spectrum, these exciting new gauges feature a stainless steel case, polished bezel, heavy-duty brass 1/8″ NPT male connector, and are compatible with 1/8″ NPT female pressure ports found in most performance fuel pressure regulators. The white face with black numbers and hash marks is easy to read and includes the Aeromotive name and logo. Two versions are currently offered; 0-15 PSI P/N 15632 and 0-100 PSI P/N 15633, and are available now through any Aeromotive dealer or at: www.aeromotiveinc.com.
That is the design of the Marshall Guage that I posted. They have always had a relief valve.
 

·
Registered
1968 GTO 400, TH400
Joined
·
19 Posts
Just a kinda for whats its worth, if you install a regulator with a mechanical pump use the dead head style or else the fuel pressure will constantly hunt not hold steady, I'm dealing with the hunting pressure right now using a return type regulator with a Edelbrock mechanical pump, I like the function of the return type regulator just to keep fuel constantly moving for cooler fuel temps. I cant remember where i read it but traditionally 6-7 psi for carbureted is what you wanted but modern fuels needed 3-4 psi to work better with carbs, so most fuel pumps will need a regulator of some kind
 

·
Registered
Joined
·
895 Posts
Just a kinda for whats its worth, if you install a regulator with a mechanical pump use the dead head style or else the fuel pressure will constantly hunt not hold steady, I'm dealing with the hunting pressure right now using a return type regulator with a Edelbrock mechanical pump, I like the function of the return type regulator just to keep fuel constantly moving for cooler fuel temps. I cant remember where i read it but traditionally 6-7 psi for carbureted is what you wanted but modern fuels needed 3-4 psi to work better with carbs, so most fuel pumps will need a regulator of some kind
Wow never knew that. I must be shoving fuel down the throat of my Z28 and Gto. What is the reasoning behind that? Kinda like a vaccine for our carbs?:eek:
 

·
Registered
1968 GTO 400, TH400
Joined
·
19 Posts
I think the needle and seats cant hold back the fuel at that 6-7 psi pressure, maybe the new fuels additives make the fuel thinner or something ??
I was only having trouble at idle and warm to hot restarts with it being really loaded up when i restarted it, the added pressure regulator fixed those problems
 

·
Registered
1968 GTO 400, TH400
Joined
·
19 Posts
No problems at WOT, it was just at idle and hot/warm restarts, I am running a Quick Fuel carb, could be a Quick Fuel thing but everything i was able to find on the web all pointed to the same fixes, reduced pressure but maintaining flow volume at WOT
I might be a little over carbed (780 with vacuum secondaries) it will blow some dark greyish smoke/cloud at WOT but I'm hoping changing the air bleeds will help that, could just be my engine, original engine never been out of the car
 

·
Registered
Joined
·
6,005 Posts
Just a kinda for whats its worth, if you install a regulator with a mechanical pump use the dead head style or else the fuel pressure will constantly hunt not hold steady, I'm dealing with the hunting pressure right now using a return type regulator with a Edelbrock mechanical pump, I like the function of the return type regulator just to keep fuel constantly moving for cooler fuel temps. I cant remember where i read it but traditionally 6-7 psi for carbureted is what you wanted but modern fuels needed 3-4 psi to work better with carbs, so most fuel pumps will need a regulator of some kind
The factory 1967 spec for non-AC cars is 5-61/2 psi at 1,000 RPM's. AC cars are 3 - 5 1/2 psi at 1,000 RPM's. The AC cars had the return line to the tank, so you can see the difference it makes. Note this pressure is at 1,000 RPM's. Below that the pressure is less because that pump is not pumping very fast to make the higher pressures.

There is no difference between modern fuel pressure requirements and old school fuel pressure requirements. The difference may be with the carb type, needle/seat type and size, return line, and even gas line diameter.

Some larger carb, dual quads, and bigger cubic inch and HP engines require more fuel than a stock pump can provide. That's where you get into electric pumps and gallons per hour flow rates, larger fuel line sizes, BUT, you still need to have a regulator to provide the manufacturer's maximum or required fuel pressures.

Seems a number of the replacement/aftermarket fuel pumps do have more than stock pressures and need a regulator so they do not over-power the needle/seat and push gas past it.

You look for more gallons/per/hour over fuel pressure. Better to have more GPH at a low pressure than high fuel pressure and low GPH flow.

So many variables to be considered - not just as simple as going to NAPA as it was in 1975 and getting a correct replacement AC Delco fuel pump that you simply installed and went about your business.

Picture 1 & 2 - are examples of a fuel pressure regulator/return line set-up.

Picture 3 - is using an electric pump to prime the carb, or get the gas to the carb - like starting it. But, you can see that the pump has a bypass line that allows you to shut off the pump and let the factory fuel pump draw gas from the tank as it normally would. How is this possible? Look at the check valve in the system. When you activate the electric pump the line is pressurized and closes off the bypass line so it can only send fuel forward to the carb. Once the pump is shut down, the pump itself becomes the shut off valve and gas is drawn past the check valve via the mechanical fuel pump on the engine and providing a normal flow of gas from the tank.

Picture 4 - If you have an electric fuel pump, you want to have a pressure switch shut off wired up so it kills the pump when the engine is shut down - just in case you had a few nips of the 'ole moonshine keg and you shut the key off, but forgot to flip the off switch to the fuel pump (if you run it constant in place of a mechanical pump or as a helper pump).

Rectangle Font Output device Parallel Brand
Rectangle Font Parallel Diagram
Motor vehicle Gas Cable Audio equipment Electrical wiring
White Font Rectangle Line Parallel
 

·
Registered
Joined
·
83 Posts
I am running a Carter M4868 from Rockauto. I installed it 8 months ago and it has been working well with no problems.
 

·
Registered
Joined
·
20 Posts
I have a 66 GTO with the Tri-Power , added the fuel / vapor return line. Took my regulator off, switch to none ethanol fuel 93 octane. Stock mechanical fuel Pump A/C Delco , runs Great.
 
1 - 20 of 31 Posts
Top