Fighting a warm fuel pressure problem on my rig that I can't seem to figure out what's going on. Holley 4 barrel, mechanical pump, phenolic spacer, 350 motor. Pressure is fine when starting 6-7 lbs., but after about 10 minutes, it is dropping to almost zero. Carb still is squirting fuel, but I know it is running lean as exhaust is popping. Before I thought it was just a bad vented cap. It was building a ton of pressure and actually was dripping fuel into intake when it was sitting and hot out. I removed the valve in the fuel cap and did drill a tiny breather hole in it too. It helped the fuel dribble and pressure, started fine, and pressure good at start, but again, it drops when the truck is run for while. This rig did have an electric pump on it when I got it, but I was hoping to stick with mechanical as I have never had a problem with mechanical other than hot vapor lock, which I have always solved with good line routing and a carb spacer. Any thoughts?
Are there any “floaters” in the tank that are getting sucked into the fuel pickup tube? Sent from my iPhone using The H.A.M.B. mobile app
I’ve not had the this experience but everyone here indicates problems finding a good reliable fuel pump. I would install the mechanical pump on that SB in a heartbeat. Where is this pump installed on the fuel line routing? IE. proximity to engine, fuel tank and filters??
Tank was dipped, so I'm sure it is clean. The pickup sock filter was gone, so I did run without, although I wouldn't think this would affect the pressure or the problem, but maybe I am wrong.
Mechanical pump on the motor. Tank to pump line is maybe 3 feet. Not far. Filter right out and after tank.
Sorry. For some reason I read you had an electric pump. Check your filter for shits and giggles. Also eliminate all variables by hooking up a gauge to your pump. It should isolate if it’s a feed problem.
Was way off on tank to pump length. Almost 7 feet. I’m wondering if I need a larger feed. It is 3/8” line right now. Filter looks good.
Bypass the tank and run a separate fuel line from a container of gas directly to the mechanical fuel pump and see if problem persists. Don't know what kind of fuel pressure gauge you are using but I have found that the glycerin filled fuel gauges will drop to zero as the heat in the engine compartment builds up. I drained out the glycerin to get accurate reading. Come to think of it, remove the pressure regulator from the system. Just run the line from the tank to the mechanical pump. Shouldn't the stock pump supply the correct amount of fuel by itself?
5/16" line is good for almost any carburated system. Make sure the suction flex line from the frame hard line to the pump is not colapsing.
Interesting on the low reading with the glycerin gauge. I took it out of the system. Maybe the carb is just running lean and this cheap liquid gauge is the issue. I'll start here for now. Thanks.
With regard to : "Shouldn't the stock pump supply the correct amount of fuel by itself?" http://www.superchevy.com/how-to/en...ou-need-to-know-about-aftermarket-fuel-pumps/ I had a 64 Chevelle with a 327 with an aspirated 4 barrel carb and only the stock mechanical fuel pump and it ran fine and dandy. No fuel regulator and no fuel gauge. Is that so unusual?
I thought I had a problem with my fuel pressure. My gauge would go to zero once the engine warmed up. So I did the obvious, replaced the gauge, still would go to zero once warm. Removed the gas cap, replaced the electric fuel pump and blew the lines to make sure they were clear. Like 19Fordy said, the problem are those small fuel gauges, they don't like the heat from the motors. The new has the rubber relieve button in the back, but doesn't seem to help the problem. I just check it when cold now.
Solid axle, drain some of the fluid out of the gauge. I wonder if you replaced the fluid with DOT 5 if it would still work ok. I didn't. Now reads a steady 4 psi which is what I need. All that glycerin does is dampen the needle movement..