This is driving me crazy, I need some help!!! I am running the same combination in my 67 for quite a few years now without any problems. It is a mildly built 350, 4 speed with a Holley 1850 600 cfm vac secondaries. The car sat for a couple of years with some treated fuel in it. I have recently started driving it and had a fuel starvation problem where I almost didn't make it back home. The old pump was all wet on the outside and I figured that it was going bad, so replaced it with a new Holley mechanical unit and installed a see through filter and pressure gauge between the pump and carb. Fired it up, filter is full of fuel and 5.5 psi, then it slowly starts loosing pressure until it wouldn't stay running. Figured it must be the sending unit, since it was the original one. Pulled it out and the filter/sock was all deteriorated so I thought that was the problem. New tank, new sending unit, new steel line from tank to pump and all new rubber fuel line sections. Fire her up and same problem. Has to be the pump right? Summit sends me a replacement. I install it and same problem. I fire it up, 5.5 psi and fuel filter is full of fuel, but it slowly starts loosing pressure and volume. What the heck is the problem. The carb is the only part of the fuel system that I have not changed. So does it just need to be disassembled, cleaned out and rebuilt or is the problem somewhere else?!?!?:confused:

Is your gas cap vented? It could be that you are developing a vacuum in the fuel tank from the fuel pump which is causing fuel flow to come to a halt. A quick test is to just take the gas cap off and see if your problem persists. Taking the cap off will create a massive air bleed into the tank which will not allow a vacuum to form in the tank.

Imagine a quart of beer with a straw and the straw is hermetically sealed to the cap. You will only get so much beer before you just can't suck anymore thru the straw.

alan

That could very well be the problem.

You have a sluggish running fuel pump push rod due to it being partially bent!....Purchase a new, straight push rod and you'll be all set!:yes::thumbsup:

Is your gas cap vented? It could be that you are developing a vacuum in the fuel tank from the fuel pump which is causing fuel flow to come to a halt. A quick test is to just take the gas cap off and see if your problem persists. Taking the cap off will create a massive air bleed into the tank which will not allow a vacuum to form in the tank.

Imagine a quart of beer with a straw and the straw is hermetically sealed to the cap. You will only get so much beer before you just can't suck anymore thru the straw.

alan
Stock, vented gas cap. I have run it both with and without the cap, no difference.

You have a sluggish running fuel pump push rod due to it being partially bent!....Purchase a new, straight push rod and you'll be all set!:yes::thumbsup:

I've had this same motor in the car for a decade or more and just replaced the fuel pump for the first time. How does a push rod get bent during normal operation? It seemed free, when I had the old pump out, the push rod just slid right out. I had to use the bolt hole in the front of the block to hold it while I installed the new one, making sure not to mar the surface by only snugging it by hand.

Well, if the push rod is not bent then it's time to disassemble the carb and install a renew kit.....Most likely the floats needle and seats are leaking!

Install a deadheaded vacuum gauge, gauge only at inlet, at the fuel pump inlet and with a full carb of fuel, see how much vacuum the pump creates. Should be a min of 15 inches of vacuum.

If it passes, then blow shop air into tank sealed with a rag at the filler neck and see volume of fuel coming out of inlet hose, should be quite a bit. No fuel, then a rubber line has been sliced when installed or kinked.

Install a deadheaded vacuum gauge, gauge only at inlet, at the fuel pump inlet and with a full carb of fuel, see how much vacuum the pump creates. Should be a min of 15 inches of vacuum.

If it passes, then blow shop air into tank sealed with a rag at the filler neck and see volume of fuel coming out of inlet hose, should be quite a bit. No fuel, then a rubber line has been sliced when installed or kinked.
I'm not sure if I follow you. First part of test, install T-fitting before pump and install vacuum gauge and read while running? Second part of test, disconnect hose to carb inlet and see how much fuel comes out when blowing into filler neck?

Yes, disconnect the inlet hose from the tank and install a vacuum gauge on the pump inlet, crank up the the engine with a carb full of fuel and see how much vacuum the pump creates.

You can 'T' the gauge with the inlet hose if you like after doing the above test and watch the gauge. There should be no vacuum created if pump is primed and no faults with the fuel supply.

Blowing air into the tank filler tube, no more than 10-15 PSI, short squirts with the air nozzle, pressurizes the tank alittle and forces fuel out the tank through the fuel line and to the pump inlet, if the inlet hose is disconnected at the pump. If there is a good flow, all is well from the inlet hose back to the tank.

Does the inlet hose at the tank have a kink in it?

Ok, ran the test as described. Steady 15" Hg. Only let it run about 45 seconds, wasn't sure if the pump diaphram would get damaged if being run dry for too long. Forced air into the tank and had a steady stream of fuel coming out of the supply line. What next?!?!?!?

Did you clean out the tank when you had it apart? Those socks plug pretty easy. Also, did you dump the old gas and start with fresh?

Good vacuum and no restrictions in the line. Now hook up the inlet hose to the pump and outlet line/hose to a qt jar or gas can and pump should fill qt jar in approx 15 seconds. Try it with tank filler cap on & off.

What happens to the see-through filter if you pressurize the fuel tank while running?
Does the engine die or keep running?

Did you clean out the tank when you had it apart? Those socks plug pretty easy. Also, did you dump the old gas and start with fresh?
Everything is new:tank, sending unit, fuel lines, pump and even the gas!!!

Good vacuum and no restrictions in the line. Now hook up the inlet hose to the pump and outlet line/hose to a qt jar or gas can and pump should fill qt jar in approx 15 seconds. Try it with tank filler cap on & off.

What happens to the see-through filter if you pressurize the fuel tank while running?
Does the engine die or keep running?
Thanks Everett, I'll run these tests today after I get done with my honeydos!

Ran the volume test with the pump. Somewhere in the 15-20 second range (lost track of time) the quart bottle was full of fuel. But I think the problem is with the carb. I tried to run the second part of the test;pressurizing the tank while running and watching the volume in the filter, but it would not stay running on it's own, wouldn't even idle, I had to nurse the throttle by hand. I had to continually actuate the throttle to keep it going, if I steadily increased the throttle then it wanted to die, if I let the throttle return to the idle position it would die. So, is it a an accelerator pump problem and if so, would that affect the volume of fuel the carb would allow the pump to provide or am I dealing with two seperate problems?!?!?!

If you had to constantly move the throttle to keep it running, then I would think the accel pump is working, you should see the squirter squiting every time the throttle opened.

If the engine cannot run on its own, whether at a fast rpm or idle, then I would think the carb needs alittle cleaning, it may be gummed up in its small passages.

Since the jar has gotten filled by the pump, it pretty much rules out the supply system all the way up to the carb fitting.

That symptom just showed up today. In fact before I tried the 1 quart volume test, I first wanted to fire it up and make sure the carb was full of fuel. Actuated the throttle, squirters squirted and reached in to turn the key, it fired right up and ran on it's own like it had been. Then I put the fuel line back on the carb to try the second test when it started acting up. I will take it apart, clean it up and order a rebuild kit tomorrow. So, if the carb is not functioning properly it can cause the fuel pressure/volume problem that I have been experiencing?

Fuel line disconnected, it runs good?
Fuel line connected, it acts up?
If the needle is stuck to the seat, as in being gummed/varnished into one piece, the pump will not fill the bowls. Are the floats set correctly? Top of the float should be parallel to the top of the bowl when the bowl assembly is turned upside down, maybe alittle more distance between the top of the bowl and the float, i.e., lower fuel level.

Yes, Floats are set correctly. If I remove the plugs from the sides of the bowls and gently rock the car side to side the fuel just barely spills out of the holes. I went back and ran the car again with and without the fuel line hooked up. Believe it or not the thing ran fine either way both idling and accelerating. So I let her run for a few minutes and it's holding pressure at 5.0 psi and the filter is staying full and then.......she starts losing pressure. I shut her off at about 3.5 psi, the filter is still full, still idling and accelerating fine. I think I'm gonna name her Christine!!!

So I let her run for a few minutes and it's holding pressure at 5.0 psi and the filter is staying full and then.......she starts losing pressure. I shut her off at about 3.5 psi, the filter is still full, still idling and accelerating fine. I think I'm gonna name her Christine!!!This drop in pressure happens whether the gas cap is on or off?

He tried it both ways Everett. See post #5.
I've been lurking since this thread started. And scratching my head. This one is really hard on egos!

Yes pressure drop happens whether the cap is on or off. I re-ran the fuel pump volume test more accurately timing it with a wrist watch. Both with the cap on or off it was the exact same volume, but after 15 seconds there was only 1/2 of a quart of fuel in the bottle. This is suppose to be an 80 gph pump which should be plenty of fuel for this motor, right? I still think this has to be carb related since today when I fired it up it ran fine once it was warm. Idled on it's own and accelerated nicely, no stumbling. I ordered a rebuilt kit from Summit, should be here in a day or two.

but after 15 seconds there was only 1/2 of a quart of fuel in the bottle. This is suppose to be an 80 gph pump which should be plenty of fuel for this motor, right? I still think this has to be carb related.One-half qt in 15 seconds at idle is good, and yes, 80 GPH = 0.33 gal per 15 seconds at a higher rpm than idle - more than enough.

Thanks Fred, for the reminder. I flat forgot cap on & off. Now, if you want to do this stunt, adapt your vacuum gauge to the flat filler tube with no cap, alum/steel plate with a nipple for the vac gauge, a section of neoprene/rubber on one side to seal the plate to the filler tube, and if you can keep the engine running long enough, see if the fuel pump will pump down the tank. Obviously, the more fuel in the tank, the less free space the pump has to pump down - but once again - its only a science project not really needed, but nice to know.

If you believe its a carb issue, you might add via the bowl vent tubes, BG 44K Fuel System Cleaner at most dealers. Add alittle, maybe 1 ounce, to the bowls, then add the rest to the tank, or better yet, add the can to the tank then add some fuel, say up to 3/4 tank and drive it.

Did you figure it out yet?

Just out of curiousity, did you happen to notice if the RPM's started dropping before or with the decline in fuel pressure? I am kind of wondering if maybe the carb is slowly running out of fuel which would cause the RPM's to drop and the slower running engine isn't putting out quite enough fuel to keep up. This would leave me to think that, as has been suggested, the needle and seat are either stuck together or maybe some crud plugging off the gas passageway in the seat.

One-half qt in 15 seconds at idle is good, and yes, 80 GPH = 0.33 gal per 15 seconds at a higher rpm than idle - more than enough.

Thanks Fred, for the reminder. I flat forgot cap on & off. Now, if you want to do this stunt, adapt your vacuum gauge to the flat filler tube with no cap, alum/steel plate with a nipple for the vac gauge, a section of neoprene/rubber on one side to seal the plate to the filler tube, and if you can keep the engine running long enough, see if the fuel pump will pump down the tank. Obviously, the more fuel in the tank, the less free space the pump has to pump down - but once again - its only a science project not really needed, but nice to know.

If you believe its a carb issue, you might add via the bowl vent tubes, BG 44K Fuel System Cleaner at most dealers. Add alittle, maybe 1 ounce, to the bowls, then add the rest to the tank, or better yet, add the can to the tank then add some fuel, say up to 3/4 tank and drive it.
I think that I'm just going to tear the carb down, clean it and install the rebuild kit and see what that does.

Just out of curiousity, did you happen to notice if the RPM's started dropping before or with the decline in fuel pressure? I am kind of wondering if maybe the carb is slowly running out of fuel which would cause the RPM's to drop and the slower running engine isn't putting out quite enough fuel to keep up. This would leave me to think that, as has been suggested, the needle and seat are either stuck together or maybe some crud plugging off the gas passageway in the seat.
I am not sure when the pressure first starts dropping, but when the pressure gets down to 1.5 to 2.0 psi then I would say that the rpm's do drop with the declining pressure.

Even if the needle and seat are stuck, how would that cause the fuel pressure from the pump to dwindle? Wouldn't the pressure remain constant?

Possible a bad new fuel pump?

alan

That's what I thought, so before I posted this problem, one of the first things I did was contact Summit and they sent me a replacement pump. Installed it and the same thing, so the problem has to be somewhere else in the system.

Even if the needle and seat are stuck, how would that cause the fuel pressure from the pump to dwindle? Wouldn't the pressure remain constant?

Possible a bad new fuel pump?

alan

My 'theory' is that the needle is allowing a small amount of gas through when the line is under pressure but not enough to keep the engine running. Once the fuel in the bowl drops, faster than the needle will flow, the engine starts dieing which slows the speed of the pump. As the engine dies the fuel pressure drops to zero. Just my thoughts on this. I would clean the needle and seat area and try it. It sounds like it is getting a kit so that, in my way of thinking, will cure the problem or give more clues.

The rebuild kit should be delivered today or tomorrow, but I am heading out of town for a week or so. I will work on it when I get back and post my findings/results.

Well it took long enough, but I finally got the carb put back together. The bowls had some residue in them and the metering plate was pretty well all gunked up, so I soaked that part, cleaned the rest and installed the rebuild kit. Fired it up, set the floats and the fuel mixture. For the first few minutes I had steady 5.0 psi and full volume of fuel in the filter. Engine was really responsive and revved nicely no hesitation. But,......you guessed it pressure started dropping and volume in filter started to decrease. This was over the course of 22 minutes both idling in the driveway and one trip through the neighborhood. Once back at the house I was down to 1 1/4 psi and hardly any fuel in the filter and the engine sounded like it was about to die. Called Holley tech support, guy told me the gauge is crap, that the carb wouldn't even run if it had less that 3 psi. So, removed the gauge, purged the line, hooked it back up and took it for a drive. Started out with just an air bubble in the filter, drove her about 20 minutes and once back at the house, popped the hood and filter is about half full of fuel, but ran great idling and accelerating. Spent some time picking things up in the garage to put the car away. Go to fire it up, there is no fuel in the filter as it is running off whatever is still in the carb, I watch as the fuel just dribbles in from the inlet side of the filter housing and the engine sounds like it is starving for fuel. WHAT THE HECK IS GOING ON!?!?!?!?!?!

Have you replaced the three sections of hoses in the inlet line?
Put a hand vacuum pump on the pump inlet hose to draw fuel?
If you put 3-5 PSI of shop air into carb inlet tubing, you should feel air escaping out of the vent tubes, if fuel level is low enough to open needle & seat.

It's gotta be a bad fuel pump, obstruciton in the pickup or an obstruction in the fuel line.

Many years ago, I have a VW that ran fine until you went up a long hill, then she would crap out due to fuel starvation. Did everything I could think of so in desparation, I pulled the fuel tank. Wedged in the outlet neck was a bead of solder that must have been left over from a tank repair 3 years ago (done by a reputable shop). I drilled out the solder blob, flushed the tank and never had a problem again.

alan

Stock, vented gas cap. I have run it both with and without the cap, no difference. Have you checked and blown threw the gas cap to make sure its not plugged up. Is the rubber hose at the pickup to the hard line kinked.

Have you replaced the three sections of hoses in the inlet line?
Put a hand vacuum pump on the pump inlet hose to draw fuel?
If you put 3-5 PSI of shop air into carb inlet tubing, you should feel air escaping out of the vent tubes, if fuel level is low enough to open needle & seat.
Yes, replaced all sections of rubber fuel line. I checked the supply line by removing it from the pump and blowing air into the tank which resulted in a steady stream of fuel. I don't have hand vac pump.

It's gotta be a bad fuel pump, obstruciton in the pickup or an obstruction in the fuel line.

Many years ago, I have a VW that ran fine until you went up a long hill, then she would crap out due to fuel starvation. Did everything I could think of so in desparation, I pulled the fuel tank. Wedged in the outlet neck was a bead of solder that must have been left over from a tank repair 3 years ago (done by a reputable shop). I drilled out the solder blob, flushed the tank and never had a problem again.

alan
It's the second fuel pump. Odds are that two would not have the same problem. Maybe 80 gph isn't enough volume to keep up? I think I might have to drop the tank again and check the sending unit. It is an OER unit, looked like a quality piece. I would like rule out everything else before doing that.

Have you checked and blown threw the gas cap to make sure its not plugged up. Is the rubber hose at the pickup to the hard line kinked.
I cannot blow outward, but I can suck through the vent. I figure it is a one-way check valve. I thought that it might be restricted, so I took the cap off after driving while the engine was still idling and the volume in the filter was very low, but nothing changed.

I cannot blow outward, but I can suck through the vent. I figure it is a one-way check valve. I thought that it might be restricted, so I took the cap off after driving while the engine was still idling and the volume in the filter was very low, but nothing changed.Well it sounds like the lobe on the cam for the mechanical pump is worn... Easy fix would be to run an electric pump...

If that is the problem, would the push rod wear before the cam lobe? If so, maybe replacing the push rod will make a difference.

Both the cam lobe, if OE are Parkerized, and push rod are hardened steel, don't think they would wear out, but always a possibilty. The end of the push rod will show defamation.

But you had already filled a qt jar pretty fast earlier in a post.

Both the cam lobe, if OE are Parkerized, and push rod are hardened steel, don't think they would wear out, but always a possibilty. The end of the push rod will show defamation.

But you had already filled a qt jar pretty fast earlier in a post.

Correct, and the push rod looked fine on the pump end and seemed to float freely in the block.

....the suspense is killing me.

For giggles, what about running a line from a bucket of gas to the fuel pump. If it works, then you have isolated the problem behind the fuel pump. Move the bucket to the back of the car and try again.

alan

....the suspense is killing me.

For giggles, what about running a line from a bucket of gas to the fuel pump. If it works, then you have isolated the problem behind the fuel pump. Move the bucket to the back of the car and try again.
alan

Sorry about the bad lobe theory just trying to help out with the possibility's.

This would help eliminate the possibility of a bad or clogged pick up. Be vary careful and make sure you do this outside not in the garage with gas fumes.

Sorry about the bad lobe theory just trying to help out with the possibility's.

This would help eliminate the possibility of a bad or clogged pick up. Be vary careful and make sure you do this outside not in the garage with gas fumes.

Good point Skip. Do it outside and make sure you have a fire extinguisher close by.

:beers:

alan

....the suspense is killing me.

For giggles, what about running a line from a bucket of gas to the fuel pump. If it works, then you have isolated the problem behind the fuel pump. Move the bucket to the back of the car and try again.

alan
Good idea. The test will have to wait a few weeks, I am out of town on a job.
I'll post the results when I get back.

I wonder if your just suckin air brfore thr pump. Rest preasure may not leak but vacume psi may. . The old one leaked, the new lines arnt sealed with the new parts. Just a thought
I had a brake line that sucked air on release and only leaked brake fluid after it heated and cooled sevral times. I never thought that could happen but.

Pretty sad, but I have been so busy with work and fixing the daughter's daily driver that it has taken me this long to finally get around to running the test. I ran a piece of fuel line from a gas can directly to the pump. Fuel filter immediately was filled and stayed that way while the car warmed up. Hooked the fuel pump back up to the hard line and moved the gas can around to the rear. Within a minute or so, the fuel level dropped in the filter. Verified that the rubber line was still submerged in the gas can, so it looks as though the culprit is the hard line itself. Have any of you had or heard of one of these pre-bent lines having a split in it or some other type of flaw. I did have to "massage" it some to get it to follow the frame around the firewall area, maybe I damaged it somehow. Tomorrow I will try blowing the line out and see if there is any obstruction in it (which I already did when it was installed) and also try to pressurize the line and look for a leak. One step closer to getting her back on the road!!!

Well, obviously, if it had a split, it would leak and show itself. Possibility of a bend that has narrowed the inner diameter of the line so it is a real choke point severely limiting flow to the pump?

alan

My stock Delco fuel pump on a sbc 350 using just the starter motor filled a quart jar in 15 seconds which is one gal per min and 60 gals/hr. 3/8" fuel line to tank. Going to replace pump with Carter GM5900P rated @120gph. Suggest you check your fuel line for damage. Inlet side of pump is pulling a vacuum while running with no pressure when off. Small leak could be hard to find. IMO
Tom Sholl

I wonder if your just suckin air brfore thr pump. Rest preasure may not leak but vacume psi may. . The old one leaked, the new lines arnt sealed with the new parts. Just a thought
I had a brake line that sucked air on release and only leaked brake fluid after it heated and cooled sevral times. I never thought that could happen but.
That's what it was, suckin air!!! I was running through the different scenarios trying to isolate the problem by first running a small gas can in the engine compartment straight to the pump. Went out and drove it, 6 psi and filter full of fuel. Moved the can to the trunk and ran it to the hard line. Went out and drove it, fuel level and psi dropped. When I disconnected the rubber line from the pump to the hard line, I noticed that the tubing right next to the flared end had some grooves on it, I suppose from the die during manufacturing. I never noticed it before, but I was really looking close at everything by this point. I just moved the the rubber line further back from the flared end and clamped it. Drove her down to the gas station to put some fresh fuel in, about a 10 mile round trip and everything seems to be fine. I can't believe that the problem was that simple after all. Anyway, thanks for everyone's input - I do appreciate it. I'll post some pictures of my ride in a few days.:hurray:

Thanks for the feedback Chris. But now we have one more thing to check for problems.;)

That's what it was, suckin air!!! I was running through the different scenarios trying to isolate the problem by first running a small gas can in the engine compartment straight to the pump. Went out and drove it, 6 psi and filter full of fuel. Moved the can to the trunk and ran it to the hard line. Went out and drove it, fuel level and psi dropped. When I disconnected the rubber line from the pump to the hard line, I noticed that the tubing right next to the flared end had some grooves on it, I suppose from the die during manufacturing. I never noticed it before, but I was really looking close at everything by this point. I just moved the the rubber line further back from the flared end and clamped it. Drove her down to the gas station to put some fresh fuel in, about a 10 mile round trip and everything seems to be fine. I can't believe that the problem was that simple after all. Anyway, thanks for everyone's input - I do appreciate it. I'll post some pictures of my ride in a few days.:hurray:

And since that point was higher than the tank, no leak. Wow, that is one for the books. Great pursuit, great, great, great.

alan

It's always a simple problem whipping our butts. Good find.