You say its running ok otherwise? I did have a problem with low fuel pressure once due to a float problem. As John said if the needle valve is open and fuel is flowing through the pressure will not build up. Process of elimination is usually good for this type of problem but this seems like a biggie! Will it stop running when the pressure gets down? What type of carb do you have? Have you checked the float level and the needle and seat? I'm not making any assumptions about your ability just trying to trouble shoot this thing in my head. Its sort of a what would I do next scenario. Good Luck.. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Charlie:

You say after 10-15 minutes the gauges read close to 0.  Is that all 3 gauges, including the outlet of the pump?  If that is the case, the pump cannot draw fuel, because of a restriction in the inlet line or no vent in the tank.  What do you find in your flow tests?  Have you tried pumping 3 or 4 gallons instead of the common pint or quart?  Does the flow start to slow down after a couple minutes of pumping?  Does the pump change its sound?  You're right, the chance of two bad pumps is slim.  I have had problems with viton needles getting softened by the alcohol in the gas and sticking in the seat.  The carb goes dry, but fuel pressure does not drop off at all.

John

John - "The Hoosier Hurricane"

I suggest you take a time out. Try by first re-stating your problem. Is it really a fuel pressure issue? Everyday millions of cars all over the world run and nobody has a clue what their fuel pressure is. So if it runs why do you care? Because IT DON`T RUN. Maybe that could be the problem? So figure out why IT DON`T RUN and fix the real problem. Then adjust the fuel pressure.

Chuck, It runs great.  It idles well until the pressure gets really low which seems to correspond with things warming up.  Then it starts to stumble and won't run unless I rev it.  If I keep it above idle, say 1000rpm it seems to do fine.  I think that he fact that it will run above idle is the key.  I just don't know how to interpret it.  It doesn't make sense that there is not enough volume to idle but it can run well at 1000, or 2500 where more fuel should be required.  I too think that a float and needle check should be performed next.  There really isn't much else.

John, the new pump is putting out 6.5psi.  When the other two gauges are at or near 0 the pump is still at 6.5.  The other pump followed the same trend.  I haven't yet done the flow test.  I wanted to try the new pump in hopes that the problem would be solved. Plus, I haven't yet made the filler parts for the tank and therefore I cannot fill the tank without removing it.  Much easier to do with a friend.  I wil check it.  It doesn't seem to slow down or change sound.  I have 13.8volts at the pump and 14.4 at the battery when it's running.  The new pump seems to operate more smoothly.  The needle of the gauge would pulsate by a little more than 1psi with the other pump.  It only pulsates by aproximately 1/4psi now.  The pulses are expected because of the pump design.  I think I'll check the flow before running the engine and then after the pressure drops.  That way I'll have a reference in addition to the rated flow.

One thing I haven't done is run a rubber line directly from the pump to the carburetor.

It is possible that the fuel pressure is not the problem but I don't know what else to look for, given the symptoms.  Persuing the pressure could be a case of too much information.  One of my older buddies told me that having a tachometer is a bad idea because "you will try to see how high it will rev and break something".  Pressure gauges could be another way to find trouble.  I am only looking at the fuel pressure as the cause of the idling characteristic because the gauge was reading low the first time it died while idling.  It did run fine for a month or so before that with low pressure, which I had written off as a bad gauge at the time.  What else could cause it to die at idle, after warming up but run fine at a higher rpm?  I may be fighting the wrong battle.

Oh, something else I've noticed is if I stop hard the engine will sometimes die.  I wonder if that may indicate that the float level is low?

Lawrenceville, GA

Look down the carb with the engine running. See if its dribbling fuel. With the float too high or needle stuck it will overflow into the carb. This will also cause the engine not to idle well and stall on quick stops. What type of carb are you running? Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

It's an Edelbrock 600.


Lawrenceville, GA

Edelbrock tech said that the carb can't be the problem. In order for the pressure to drop the needle would have to be stuck open which would be apparent by flooding and fuel coming out of the float bowl vents, which is not happening. That's what I had figured. I'll still check the float levels tonight and make sure nothing is in the passage of the carburetor. I haven't done that in a while anyway. I'll get some more rubber hose and run it directly from the pump outlet to the carb, and ensure that it is nowhere near anything hot and just start from square one. Maybe I've overlooked something so I'll just go back and do it again.


Lawrenceville, GA

Another way to return to basics is to eliminate the entire fuel delivery system by using a small container of gas and a rubber line to your carb. Put the container above the carb and use gravity to fill the fuel bowl. Observe the usual safety precautions and a pint or so of gas. Work up from there. A lot of model A fords used a similar system.

I checked the carb. The float levels were slightly off but not enough to cause problems.

You know what else I haven't done? I haven't checked the pump voltage when the pressure has dropped. It could be the switch. I have a .6 volt drop between the + side of the switch and the - side of the switch with everything cool. This is taken at the spade terminals of the switch. I don't know if that's what should be happening. I think I'll check that first thing when I get home this evening. If the switch is faulty and dropping the voltage several volts, the pump might maintain pressure at the outlet but not supply the volume to maintain pressure 15 feet away. Let's hope so.


Lawrenceville, GA

The voltage is good when the pressure is low.  I ran rubber line from the pump outlet, directly to the carb inlet with a gauge just before the carb.  I ran the line along the passenger side, completely avoiding the exhaust and allowing for the shortest possible length of hose running across the engine.  The same thing is happening.  I just can't understand what's going on.

I'm going to try the old, reliable mechanical pump tomorrow. 

Lawrenceville, GA