Can a stock fuel pump produce too much pressure?

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Kern Dog

Kern Dog

Build your car to handle.
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I have a strange situation here.

I have a stock 360 in a Duster, it has a Weiand 4 barrel intake and a Holley 600 single feed VS # 1850 carb. The Holley was rebuilt a couple of years ago but the car has been sitting. I've had this car here since 2007 as a project with my brother in law who lost interest in it years ago.

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This car will start and run, but within moments the engine starts to sputter and fuel starts puking out of the vents, then out of the boosters. Of course, it stalls and won't restart until the fuel evaporates in the intake.
Float level too high?
I adjusted it and it still does it. I pulled the carb apart, soaked it awhile, blew out the passages and put it back together with a new power valve and needle valve.
It still puked fuel. I tried another carburetor, a Rebuilt ThermoQuad. Yeah, that one pukes fuel too.
I have no gauge to test the pressure but the inline fuel filter isn't getting full or bulging, it looks fine.
I'm going to try another carburetor on this engine tomorrow, maybe the one from Jigsaw. I know that one is fine.
This is weird though. I've never dealt with this before.
 
Vacuum / pressure gauges are cheap

Technically the mechanical fuel pump can only produce as much pressure as the internal spring can produce.

Unless it is a special pump for some reason I would always no, it can't produce too much pressure.
 
Kern Dog said:
I have a strange situation here.

I have a stock 360 in a Duster, it has a Weiand 4 barrel intake and a Holley 600 single feed VS # 1850 carb. The Holley was rebuilt a couple of years ago but the car has been sitting. I've had this car here since 2007 as a project with my brother in law who lost interest in it years ago.

View attachment 1716275281

This car will start and run, but within moments the engine starts to sputter and fuel starts puking out of the vents, then out of the boosters. Of course, it stalls and won't restart until the fuel evaporates in the intake.
Float level too high?
I adjusted it and it still does it. I pulled the carb apart, soaked it awhile, blew out the passages and put it back together with a new power valve and needle valve.
It still puked fuel. I tried another carburetor, a Rebuilt ThermoQuad. Yeah, that one pukes fuel too.
I have no gauge to test the pressure but the inline fuel filter isn't getting full or bulging, it looks fine.
I'm going to try another carburetor on this engine tomorrow, maybe the one from Jigsaw. I know that one is fine.
This is weird though. I've never dealt with this before.
Click to expand...
Read my response on FBBO.
 
I have a weird high pressure issue with my Duster, it will go to 9 psi with a Carder muscle car series pump, specs show it at like 5 psi for the pump.
But it does not seem to affect the carb.
I am thinking the gauge maybe got some residual 93 ethanol gas, that gummed up the gauge readings.
But the gauge will go back to zero. Maybe the gauge is right????? and the carb 625 street demon is tolerant of it.

The high pressure readings did not start until the car sat over the winter with ethanol gas in it.
 
I know that my son had issues with his pump he thought .
His Holley would run high in the bowls .
He adjusted the fuel regulator down to less than 5 pounds,,,,,same problem .
He adjusted the needle and seats down to where the fuel was well under the sight plug .
Drive it some and check,,,,always high .
Adjusted several times,,,,,never could get it right .
We could see the level low in the bowls,,,,,but it still would get high after a drive
He finally swapped the front needle and seat with a brand new Holley version,,,not aftermarket .
Fixed the front bowl,,,,,then swapped the rear needle and seat too .
Guess what ,,,,,no overflowing now .

Might not be your problem,,,,,but it’s worth a look !
I would also suggest having a regulator ,,,,,it’s good insurance .

Tommy
 
With the Holley, I pulled the needle and seat and replaced it. It seemed to run the same. I removed the side plug in the float bowl and fuel drained out so I adjusted the float setting. It still seemed to puke out the vent tube.
The ThermoQuad does the same thing. The ThermoQuad has maybe 15 minutes of run time on it since it was rebuilt.
At least a year ago I decided to tinker with the car a bit. I couldn't keep it running because I wasn't getting fuel up from the tank. I went to the shed and grabbed a shiny looking pump and swapped it in. I have collected parts from friends and acquaintances for years and often times, I don't remember where a lot of this stuff came from. I don't recall any special markings on this one to denote any high volume design.
I have a few other cars here with Holleys that all run great. I can pull carburetors off of any one of them to test on the Duster.
It was 111 when I was out there working on the car. Usually I think of trying parts from other cars but maybe the heat was getting to me.
 
Kern Dog said:
With the Holley, I pulled the needle and seat and replaced it. It seemed to run the same. I removed the side plug in the float bowl and fuel drained out so I adjusted the float setting. It still seemed to puke out the vent tube.
The ThermoQuad does the same thing. The ThermoQuad has maybe 15 minutes of run time on it since it was rebuilt.
At least a year ago I decided to tinker with the car a bit. I couldn't keep it running because I wasn't getting fuel up from the tank. I went to the shed and grabbed a shiny looking pump and swapped it in. I have collected parts from friends and acquaintances for years and often times, I don't remember where a lot of this stuff came from. I don't recall any special markings on this one to denote any high volume design.
I have a few other cars here with Holleys that all run great. I can pull carburetors off of any one of them to test on the Duster.
It was 111 when I was out there working on the car. Usually I think of trying parts from other cars but maybe the heat was getting to me.
Click to expand...
Does the diaphragm have screws around the perimeter holding the pump together? If so, it could very well be an HP pump that needs a regulator.
 
There are different "stock" pumps. I have seen some that claim 8psi and others that claim 5-6psi. You choose.
 
I seem to recall that the pump just looked like any parts store type of pump. I'll get a better look tomorrow.
Thanks for all the input, guys. Even an idea that is a bit out there can be worth looking into.
 
There are also stock looking pumps that could require a regulator. Summit has some in the 7.5 PSI range.
 
Two carbs flooded so it is most likely the pump. Like anything man-made they can fail. Maybe some debris under the pump valve causing excessive pressure?
 
Bewy said:
Two carbs flooded so it is most likely the pump. Like anything man-made they can fail. Maybe some debris under the pump valve causing excessive pressure?
Click to expand...
Bewy, that is a good point. When symptoms aim in one direction, that is usually the problem.
 
Yes a mechanical fuel pump can make to much pressure if the diaphragma gets old and stiffer, it acts like a second spring. I had this issue on a old Mercedes, luckywise there was a note in the workshop manual!
 
plymouth4onthefloor said:
Yes a mechanical fuel pump can make to much pressure if the diaphragma gets old and stiffer, it acts like a second spring. I had this issue on a old Mercedes, luckywise there was a note in the workshop manual!
Click to expand...
Yeah, as in being soaked in ethanol for too long.
 
RustyRatRod said:
Yeah, as in being soaked in ethanol for too long.
Click to expand...
Holy crap, you think that is it?
Ethanol is all we have here. I often have to replace rubber fuel lines here because they rot out after a few years. I have a few running cars that sit many months between uses. I've had to rebuild the carburetors in them a few times.
It is my own fault...I think I'm going to drive them more than I get busy with other things. I should just default to using Sta-Bil in everything that isn't driven a couple times a month.
 
My neighbor has a 57 Chevy, been sitting for a few years. Had a problem after he got it running of the 600 Holley carb doing the same thing you described. After he worked on it a few days, I put a fuel pressure gauge in the line to the carb. It had 12 psi of fuel pressure with the stock fuel pump. So it is possible that you have a fuel pump over pressuring the carb
 
plymouth4onthefloor said:
Yes a mechanical fuel pump can make to much pressure if the diaphragma gets old and stiffer, it acts like a second spring. I had this issue on a old Mercedes, luckywise there was a note in the workshop manual!
Click to expand...
That could be a cause but we had a new one out of the box put out over 10.
 
I had to install a regulator on my "stock" Carter mechanical pump. It would go up to 9psi at as the engine rpm's went up. My Holley DP didn't like it. Running at 5-6 psi now and the carb likes that much better.
 
I didn't put a gauge on the line. I thought that maybe with two carburetors showing the same symptoms that maybe the pump was pushing too much pressure.
It looks like this:

A4EDEE0C-E5EF-4B57-AA4C-102FC062CE9F.jpeg


No cast in identifying marks, just the ink printed marks you see here.

ABDE3925-8019-44D9-A904-EEAC51315387.jpeg



4B162B18-7F6D-48E4-B414-788EAB25C1E5.jpeg



432DA888-1145-4B60-AA58-5350631FB51C.jpeg



I changed to another one that looked similar.

2F6BDE66-C3A4-4980-99FE-EAC433BF4D79.jpeg



Delphi?

26B4655C-1BC0-4498-9102-60508D480183.jpeg



It started and ran fine…. Then started puking fuel through the inside of the ThermoQuad.

90A0AD04-60E1-45E8-A9E3-6EB82AACCC30.jpeg


It was the same as with the other pump.

0F5D4474-6A77-4319-B458-DFE58754D3C7.jpeg


Once the fuel evaporates, the car starts up fine and then floods over again. I ran out of time to try a known good carburetor.
The threaded fitting on the pump that feeds the carburetor has a leak. As I tightened the line, the pump body twisted a bit.
Two pumps, same symptoms.
I'll put the first pump back in and try a carburetor from another car.
 
Kern Dog said:
Holy crap, you think that is it?
Ethanol is all we have here. I often have to replace rubber fuel lines here because they rot out after a few years. I have a few running cars that sit many months between uses. I've had to rebuild the carburetors in them a few times.
It is my own fault...I think I'm going to drive them more than I get busy with other things. I should just default to using Sta-Bil in everything that isn't driven a couple times a month.
Click to expand...
It could well be.
 
The M6866 is an old Carter muscle pump. It's rated at 7.5 PSI. That Delphi, the only rating I could find on it is 8 PSI. I found that here:
Keep in mind though, those rated PSI numbers are "supposed" to be rated at free flow. So when they are installed and pushing against the fuel system, the PSI is less. I've never liked the free flow rating method. It's not very accurate, because you don't know how much PSI is lost pushing against the fuel system.
 
Thanks, Rob. Looking those numbers up took some time. That was considerate of you.
 
Kern,
Only three things can really cause internal flooding of the TQ. All are easy to fix. Most likely are the rubber washers that seal the air horn projection to the black body. They sit in the black body, are black [ hard to see ] & are 'in the' hole adjacent to the pri main jet. Other things: fuel logged float or worn/leaking needle & seats.

If it is just the washers, just buy fuel resistant standard O rings 3/8" OD & 1/16" wall thickness. I always use these, never the ones that come in the lit, too flimsy.
 
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