# Fuel pressure (1965 tri power)



## cij911 (Oct 25, 2017)

So my car is running fine (for now) but I just installed a FP regulator and inline gauge and my pump appears to be putting out less than 3 psi (regulator maxed) !!! John from Pontiac Tripower suggested that I install a FP regulator and gauge to limit the FP pressure to ~3.5 psi (which he feels is ideal for the tri power setup). I had always thought it was supposed to be more the 6-8 psi. Also, the FP gauge needle is really bouncing (I know the car has a mechanical FP, but all cars I have ever seen with FP gauges are much smoother). 

My question is did the factory fuel pump only produce ~3 psi or is there a problem with my pump / setup ? (It appears the new FP are cheap - sub $40 and probably fairly straight forward to replace.) The car runs fine and AFRs are good right now. I am just wondering if it is a matter time.....

Thanks


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## Bob Young (May 27, 2018)

5-6.5 psi is what's called for. Also check your flow rate as that can be an issue as well.


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## cij911 (Oct 25, 2017)

Bob Young said:


> 5-6.5 psi is what's called for. Also check your flow rate as that can be an issue as well.


To check flow rate, I am guessing you mean install an inline gauge ? Not sure how I would do that, but I will look into it.

So it sounds like my fuel pump is on the way out ??


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## Bob Young (May 27, 2018)

The easy test is take the inlet to the carb off and connect a rubber hose long enough to reach a safe place outside the engine compartment, then put the hose in a coffee can and have someone start the engine. You should have a steady forceful stream into the can (at least a pint) . If it starts out good then falls off in less than 30 sec, then check the sock in the tank for being restricted. These are old cars. Just had a old chev with a plugged sock and it would run but not very well under load, changed the fuel pickup tube and pump and now runs 4-0.

Oh, just to make sure you know, fuel is flammable, be careful when spraying it around a hot engine


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## cij911 (Oct 25, 2017)

Bob Young said:


> The easy test is take the inlet to the carb off and connect a rubber hose long enough to reach a safe place outside the engine compartment, then put the hose in a coffee can and have someone start the engine. You should have a steady forceful stream into the can (at least a pint) . If it starts out good then falls off in less than 30 sec, then check the sock in the tank for being restricted. These are old cars. Just had a old chev with a plugged sock and it would run but not very well under load, changed the fuel pickup tube and pump and now runs 4-0.
> 
> Oh, just to make sure you know, fuel is flammable, be careful when spraying it around a hot engine


I have a new filter, new sock, and new pickup, so I doubt that is the issue. I know it is flowing good enough to maintain AFRs (logging with a wideband), so if I were to check flow I would do so a tad more accurately :grin2:....No idea how this method would work anyways as the FP is mechanical and thus the car needs to be running for the FP to work (unless you are just cranking the car for 10 seconds and measuring output )....

My guess is the pump is on the way out (may be original) and is definitely ancient.

Thanks for your help.

Chris


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## Bob Young (May 27, 2018)

Back in the day didn't have a method to do that, only checking plugs for proper color 

You can have weak pressure and flow and if a flat lander might be able to get around ok. Living around hills would be a different animal. Trying to make it up a pass like the Siskiyous or Blue mountains you would definitely have an issue! 

There should be enough fuel in the bowl to run the car for at least 30 sec at idle. I don't know of a spec back in the day other than the rule of thumb being "at least a pint in 30 sec". I just watch the flow and can tell when it's not enough. Guess almost 50 years of dicking around with carburetors/engines something has to rub off...

If you have already done the work of checking the tank, next would be the pump and I would also replace any rubber lines you have not replaced yet. LOL, 53 years is a lot to ask of rubber 

Good luck! Let us know what you find.


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## PontiacJim (Dec 29, 2012)

I would simply replace the pump just for good measure. If original, or even an older replacement, the pump's rubber diaphragm is most likely not compatible with ethanol fuel anyway and is/has deteriorated. For the price, and not too hard to replace, I would opt for an updated fuel pump that is ethanol friendly - and make sure all rubber lines are also ethanol compatible. 

Assume that your needle in the carbs are also upgraded to the ethanol compatible type. I also assume that FP might fluctuate somewhat as the bowl fills/empties thus opening the needle and seat as needed- especailly when all three carbs are being used.


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## cij911 (Oct 25, 2017)

PontiacJim said:


> I would simply replace the pump just for good measure. If original, or even an older replacement, the pump's rubber diaphragm is most likely not compatible with ethanol fuel anyway and is/has deteriorated. For the price, and not too hard to replace, I would opt for an updated fuel pump that is ethanol friendly - and make sure all rubber lines are also ethanol compatible.
> 
> Assume that your needle in the carbs are also upgraded to the ethanol compatible type. I also assume that FP might fluctuate somewhat as the bowl fills/empties thus opening the needle and seat as needed- especailly when all three carbs are being used.


Thanks Jim! Would a Carter unit be fine https://www.summitracing.com/parts/crt-m4566/overview/year/1965/make/pontiac/model/gto/submodel/base ?



Chris


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## PontiacJim (Dec 29, 2012)

cij911 said:


> Thanks Jim! Would a Carter unit be fine https://www.summitracing.com/parts/crt-m4566/overview/year/1965/make/pontiac/model/gto/submodel/base ?
> 
> 
> 
> Chris


Although the Summit description does not indicate if the rubber diaphragm is compatible with ethanol gas, it seems to be according to this Hot Rod article - so yes, looks like a good one: Pontiac Fuel Pumps - How To Select The Right Fuel Pump - Hot Rod Network


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## Joe'sToy (Mar 9, 2012)

Just my 2 cents, but when I rebuilt the 400 I had in my '65 I replaced the fuel pump with a Holley one. Ended up seeping fuel from the tri-power because the Holley was pushing 5-7 psi and the Tri-power floats were being overcome. I installed a Holley fuel regulator before the inlet, which was set at 3.5 psi and never had the float issue again. My tri-power was a '66 version and had been refurbished by PontiacTripower.com, Pete I think.

Joe.


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## cij911 (Oct 25, 2017)

Joe - Your experience matches what I have been told by the Tri Power gurus and apparently they run best around 3 - 4 psi. Anything greater can and will cause problems apparently. Interesting......


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## Kjruhl (Jun 9, 2018)

Hi everyone! Just joined so I can weigh in on this topic. 
I run a tri power also. It was rebuilt by Pontiac tri Powers. It is also a 66’ version. I have many thoughts and questions on this topic. 

1. Ran a tri power for many years in the distant past and never had any problems or weeping. 1/4 mile track and street. Factory fuel pump. 

2. I decided on Following the stated advice of 3-4 psi from Pontiac Tri Powers, I regulated my pressure down. I also run a Holley mechanical pump

3. Currently I am having a huge problem with running out of fuel at the top end of the track. Only an 1/8th mile track now. I get through first gear at max power, then at the top edge of second I start to feel the loss, then in third it feels like the engine starts to shut off and noses over. Then after a moment of coasting everything is fine because the bowls have filled back up. 

So here are my questions. 
Pontiac never produced specific fuel pumps based on the fuel systems. There was never a “Tri Power Pump” just to suit that specific delivery system. From what I have found it seems that all the factory pumps put out around 5-7 lbs presssure. So why would the carbs weep now if we put more then 3-4 lbs of pressure on them when they didn’t weep from the factory? Fuel pressure was not regulated decades ago when they were created. 

Many years ago when I ran the tri power I had a factor fuel pump that was originally a 4brl car. No problems then. Plus, floats and needle valve ability to stop fuel doesn’t change just because it’s a 2 or 4 barrel carb. 

So I too am looking for answers as to why should the pressure be regulated down to such a low level?


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## Bob Young (May 27, 2018)

Back in the day I never had an issue after overhauling the carbs. Pumps put out the same 4bbl/ tri power. Used OEM kits with steel needles and brass seats. Using hard lines to the carbs keeping rubber lines to a minimum on the pressure side. Set the float and drop exactly to spec and use proper torque when attaching the base to bowl and bowl to top.
Make sure the pump is putting out proper pressure and flow (flow very important and more often missed).
Hard to get good leaded fuel these days but you can always mix race fuel, 100LL or Torco to get what we had at the pump in the 60's.

I've had Tri power Goats and even a Buick once and even tho they ran good when I had them, I much prefer the single 4 that came out for 67 then fooling around with 3x2's.

Good luck!!


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## PontiacJim (Dec 29, 2012)

Kjruhl said:


> Hi everyone! Just joined so I can weigh in on this topic.
> I run a tri power also. It was rebuilt by Pontiac tri Powers. It is also a 66’ version. I have many thoughts and questions on this topic.
> 
> 1. Ran a tri power for many years in the distant past and never had any problems or weeping. 1/4 mile track and street. Factory fuel pump.
> ...



Are you running 3/8" fuel line & tank pick-up lines? Some cars did run 5/16" and in my opinion would be too small to supply the tri-power. There is a "sock" at the end of the pick-up line in the tank and if this has never been replaced - could be bad. 

Fuel filter good and one that flows? 

Other things to check are correct vented gas cap or vented gas tank. ALL old rubber lines replaced with ethanol friendly gas line. Ethanol deteriorates the old type rubber lines and you could have a hole/tear or collapsed hose that looks good on the outside.

Check for any pinched lines which could limit flow.

As best I can tell, factory pumps were 5-7 pounds. Pontiac did offer a 12 pound fuel pump with their Super Duty 421 for Nascar service. Stock pump should be fine unless you went with a bigger cubic inch engine or radical cam. Never had any fuel issues with either tri power or Q-Jets that I ran on the stock engines and never had to regulate the fuel pressure. Bump your pressure up to 5 pounds and see what happens.


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## Kjruhl (Jun 9, 2018)

It was a frame off restoration and has only 8k miles in it. Everything is new. Include by the tank and lines. I am going to pick up the high rates regulator and run high pressure like you suggest. That article link someone posted earlier from Hot Rod magazine is pretty interesting. Pontiac engineers were smart. The factory fuel pumps ran at 2 psi until 1800 rpms and then it kicked up to 7psi. Which answers the question as to why factory pumps didn’t cause weeping. Until the fuel was needed it didn’t get supplied


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## PontiacJim (Dec 29, 2012)

Kjruhl said:


> It was a frame off restoration and has only 8k miles in it. Everything is new. Include by the tank and lines. I am going to pick up the high rates regulator and run high pressure like you suggest. That article link someone posted earlier from Hot Rod magazine is pretty interesting. Pontiac engineers were smart. The factory fuel pumps ran at 2 psi until 1800 rpms and then it kicked up to 7psi. Which answers the question as to why factory pumps didn’t cause weeping. Until the fuel was needed it didn’t get supplied


Yes, that is correct - have the same article that mentions that.


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## Bob Young (May 27, 2018)

Here is the old Hot Rod article if you need to link for future reference.

Pontiac Fuel Pumps - How To Select The Right Fuel Pump - Hot Rod Network

Here's a hot tip for you guys, check this link:

https://carter.opticatonline.com/?q=

Then run the Carter number on Amazon and that gives you a pretty good price. BTW I think all the Carter pumps are now manufactured in South Korea....


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## cij911 (Oct 25, 2017)

Kjruhl said:


> It was a frame off restoration and has only 8k miles in it. Everything is new. Include by the tank and lines. I am going to pick up the high rates regulator and run high pressure like you suggest. That article link someone posted earlier from Hot Rod magazine is pretty interesting. Pontiac engineers were smart. The factory fuel pumps ran at 2 psi until 1800 rpms and then it kicked up to 7psi. Which answers the question as to why factory pumps didn’t cause weeping. Until the fuel was needed it didn’t get supplied


Unfortunately the Carter pump information does not specify whether it limits PSI below 1800 rpm.

Do yo have a wideband to monitor your AFRs? Do you have a fuel pressure gauge installed so you can confirm the pressure you are getting?


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## cij911 (Oct 25, 2017)

OK just to confirm, the aftermarket (non-AC) fuel pumps seem to be different (or at least the two I tested) - Carter and Airtex. I was getting ~6 psi at idle. I have a Holley fuel regulator installed and have the FP turned down to ~4psi (recommended by John at pontiac tri power). I have no indication of fuel starvation running through the gears, but did not have the wideband installed so I cannot confirm AFRs. (Also my runs were 1-2-part of 3rd, so maybe there would be a problem at the top of 4th.....I will confirm next weekend.)

Here is a great article I found : http://phscollectorcarworld.************/2017/10/phs-tech-files-vintage-pontiac-fuel.html


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## RunninLeMans (Apr 3, 2014)

I had the issue with the original 5/16" fuel line that came with my '64 LeMans, ran out of fuel about halfway through third gear. Changed it to 3/8" and the problem went away.


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## geeteeohguy (Feb 2, 2008)

Been running the original tripower on my '65 for the past 37 years. The previous owner ran it since the car was new. No issues at all running the stock Carter pump which puts out 5-6 psi. The last time I fiddled with the carbs (rebuild kitted them) was in the mid 1980's. Reliable as an anvil. So is the '66 Unit that I have on the bench that I've run on other cars, also with cheap, old, generic, non-regulated Carter or AC fuel pumps. The float level has to be set correctly, and the float drop does, too. Original needle valves were all brass, replacements have rubber tips. I know that the new ethanol laced fuel boils off quickly on heat-soaked engines....perhaps this is partly to blame, although I have had no issues with my '65 with e-10, which is all that's available. My old '61 Corvette with dual 4's boils off the fuel every time the car sits for 10 minutes on a 90 degree day, though.


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## RunninLeMans (Apr 3, 2014)

I have a related issue, my fuel pressure is all over the place. I was doing some test runs with my new tri-power setup and stopping to adjust idle screws and throttle stop and noticed that sometimes the pressure is 6 psig, once it was 2 psig, once it went to zero but was happily idling like nothing was wrong. Air cleaners were off and there was no excess fuel being squirted around. Last night after re-assembling after sealing the butterflies with that goop from Wright's Tripower the pressure was up around 9 pisg for several minutes, then settled down to about 7. I bought the Holley regulator mentioned here, but is this much variation normal or does it say something about my fuel pump? I understand that sometimes the bowls are filling and sometimes not. Also, after 30 years of looking at pressure gages in paper mills this doesn't look like a bad gage issue to me. But, for $15 I might replace it just in case.


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## Lemans guy (Oct 14, 2014)

If you have a glycerine filled fuel pressure gauge the glycerin gets hot and they give very unreliable readings. When fuel gets very hot it does thin a bit just like oil, I notice about 1/2 PSI when fuel real cold to real hot.

But if you stop the car and get out to check stuff those fuel lines and gauge heat soak fast, the filter as well. The pure gas has a distillation curve for summer blend around 170, the E-10 (which I run) around 140 degrees, it gets real hot in steel fuel lines and filters fast and fuel will boil in the lines, that will drop pressure and will vapor lock if bad enough.

But at 2 psi and normal operation you may just have very hot lines and gauge, with the heat effecting the reading, and the viscosity of the fuel slightly effected.

Try a better gauge don’t use glycerin filled ones and wrap the lines in some heat wrap like DEI has, or some insulator material to test.


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