I am having constant fuel pressure problems since I've swapped from TPI to carb recently. When u first start the car u have plenty of pressure. Once u go drive around a little u have little to no pressure. When I first started I was running manual pump and no regulator. Then I added a regulator. I thought that not recirculating the fuel was letting it get to hot so I replaced the regulator with a bypass style and hooked the return back up. Then I thought it might be a problem with the manual pump so I hooked up a holley red pump by the tank. Then I replaced the holley red with a factory TBI electric pump in the tank. With all these different pumps and regulator combinations it's been the same result. Initial cold start up u have plenty of pressure. Once u drive around a little u have no pressure. U have to crank the regulator all the way up and then I only get 3 psi. Any suggestions?

 

I'm going through the same thing with my GMC (avatar), Replaced everything just like you did. Truck still runs fine even showing 0 pressure, Next step when I get to it is replace the cheap oil filled Summit brand gauge.

What's the chances of all these different pumps and regulators being faulty ?

 

I would run just one pump. The mechanical pumps are good and reliable for a carb. I would remove the pump from the tank and use a modified pickup or a carb pickup. You can eliminate the return if you use a deadhead style regulator.

 

Z28 Guy has already tried that combo, I'm sure from reading his thread he's only running one pump being a TBI pump 9 to 12 lbs with a return regulator as I am.

With all the different combos tried between him and myself is why I suspect faulty gauges, He mentioned nothing about run issues while at 0 pressure. My truck has had 200+ miles put on it since my gauge started going funky......

 

The only time I've seen this problem is when people mount an electric fuel pump too high. It needs to be below the fuel level and be gravity fed.

 

Well it's now the the TBI pump with the new bypass regulator. I believe my carb might be getting to hot. I am going to make room and get a spacer and put a gauge on my line before he reg to do a test. I took the feed to the carb off today when it was showing 0 psi. When I undid the line there was a substantial amount of vapor to come out before gas did. The line later flowed great unhooked when I turned the pump on. His is also right where the gauge is located. The return was also showing great flow as well. I think I'm having vapor lock around the gauge or also in the carb as well. I've also tried 2 gauges both summit liquid filled one being new. And both times when the condition was happening it let out lots of vapor.

 

I've never experienced vapor lock and I also live in the deep south.

 

I don't think it's vapor. It is more likely air bubbles.

 

Hmmm...... That blew my gauge theory out of the water !

Mine was a Holley red pump mounted below the fuel level with non bypass regulator when I bought it, It ran fine like this for 8 years (knew the PO) but the pump rattled like crazy (likely due to too much back pressure).

When I swapped the MPI tank/pump to TBI tank with new in tank pump 3 years ago I installed the bypass regulator with a new gauge and steel braided lines, Just the middle of last summer did I notice the pressure running low. I replaced the regulator since I had a new back-up but had the same results so figured it a gauge issue.

If you figure out whats causing this issue I'd surely love to know.....

The way it is now, As long as mine runs without any issues and gets me to shows, I'm not going to park it......

 

Well I'm about to put another gauge on the pump side of the regulator and see my results.

 

Well the gauge that I put between the pump and reg is showing half a pound of pressure less than the one by my carb. Also fuel pressure is going down as the engine warms up. Also not noticing any running problems with the low pressure so I'm still puzzled. I'm really getting frusterated cuz I want to get a good tune on the car so I can take it to the track but with inconsistant fuel pressure I can't tune. But on the other hand if it ain't broke don't fix it but its gonna drive me crazy reading 0 psi

 

Run a pump from a bucket of fuel and see if the pressure goes up. Maybe theres a kink in the line.

 

Well I'm pretty sure there are no kinks, but I am going to take ur other advise and run it up to temp with a gas can and a pump so I can eliminate the tank and lines to see if the problem still exists.

 

Did you figure this out?

 

Nope not yet haven't had the time or money yet. Car has been driving fine so I've been procrastinating.

 

If I follow, are you still using rubber lines to go into the regulator? Sometimes, the barbs cut the rubber when you push the hoses on, creating a blockage to the flow. This happened on my return line and messed up my pressure reading. Also make sure your fuel filter is clean/new.

If you run any kind of electric pump, DO NOT include a manual pump. You must run a return line with a electric pump, especially an in-tank pump.

I burned out two holley black pumps using them inline with the factory fuel lines. The reason being, the factory lines pull up and out of the top fo the tank, then down to the pump which I had mounted to my frame rail. When shut the car off, the fuel would retreat back into the tank. This would cause the pump to run dry for a few seconds which is very, very bad. Caused the pump to get hot and burn up.

You're pressure should be 4.5-6psi for a carb. Anything more will flood the carb. Anything less could cause issues under acceleration or cornering as the bowls of the carb will run dry.