Fuel System: Correctly Checking Fuel Pump Pressure for 1963 Avanti R2

[HB63A2]

I have the shop manual for the Avanti and found the procedure for doing a fuel pump pressure test including the disconnection of the fuel pump-to-supercharger air pressure line at the supercharger. I bought a fuel pump pressure test gauge, but it doesn’t have any of the correct fittings necessary to hook it up as described in the shop manual. The manual says to disconnect the fuel line at the pump side of the in-line filter and hook a pressure gauge to the fuel pump line. It looks like I’ll need to get a barbed hose brass reducer to go from the 5/16” fuel line hose to the ¼” hose that connects to fuel pump pressure gauge.

Since I haven’t done this before, would it be a good idea to put hose clamps at each of those connections when I do the test? Once the gauge is connected the manual says to run the engine on the fuel in the carburetor at approximately 1000 rpm and check the pressure reading. It doesn’t say how long to run it to get an accurate reading. Those of you who have done this before, how long do you run the engine? Since the carburetor would be disconnected from the fuel line I wouldn’t think it would run too long, but how long is long enough to get an accurate reading? The manual says the pressure should be 5-1/2 to 7 lbs. Has that pressure reading corresponded to what you find acceptable? Do you have any other tips to obtain an accurate pressure reading other than making sure the fuel pump-to-supercharger air pressure line is disconnected at the supercharger?

The manual for the fuel pressure gauge says the gauge should hold the reading for one or two minutes after the engine has been turned off. Has that been your experience? I only ask that because I may not have an assistant to read the gauge while the engine is running (recently I have had to keep my foot on the gas when the engine is first started to keep it from stalling, hence I can’t get out of the car to check the pressure while the engine is running, but that’s another problem).

Thanks in advance for any guidance in safely obtaining an accurate fuel pump pressure reading!

HB63A2

[bensherb]

I'd warm up the engine 'until it will idle without you in the car, then attach the pressure gauge and run it. It might run 5 minutes without a fuel pump which should be plenty long enough to reach and read the fuel pressure.

[StudeRich]

OR, to speed it up, stick a screwdriver behind the Throttle Bellcrank stop screw at the back of the Left Cylinder head or the Carb. Idle screw.

OR, first Fix the issue with the Carb. or the Ignition that causes the stall.

Why do you feel you need to test the Fuel Pump Pressure?

Replacement Fuel pumps over the last 60 years, will not produce the same pressure as the Original Carter Pumps
noted in the Shop Manual anyway, could be More OR Less depending on the strength of the Diaphragm Spring.

[HB63A2]

Thanks all for your comments and suggestions. To answer the question about the need to check the Fuel Pump Pressure, it goes back to carburetor problems. After the car sat for about a month I went to start it and it started right up, but would not run without my foot on the gas pedal, even after it was up to operating temperature. I took my foot off the gas and it stumbled and died. I got out and was surprised to see that the carburetor leaked a significant amount of gas (luckily no fire)! I took the bonnet off the top of the carburetor and the secondary butterflies were wet. I could see a residue of gas around the Air Horn Gasket in-between the Air Horn Assembly and the bottom part of the carburetor as well as around the accelerator pump.

People suggested that it might be debris in the inlet needle valve, inlet valve that has a hardened tip, a stuck or sunk secondary float. I described my problem to a person that rebuilds carburetors and the amount of fuel that suddenly leaked out. In addition to the other comments, he questioned if the fuel pump pressure was too high. The fuel pump had been replaced with the correct one for a supercharged Avanti just before I bought the car about four years ago. He said he had worked on other cars recently with fuel spillage and seepage similar to mine and tested the fuel pumps to find that they had excessive pressure (over 6 lbs.). He surmised that recent rebuilt fuel pumps are just junk and suggested testing the fuel pump pressure before tearing into the carburetor.

Have any of you had excessive fuel pump pressure problems with your Carter AFB carburetors with superchargers? I’d hate to tear down the carburetor if the real problem was the fuel pump!

Thanks in advance for any comments or suggestions to solve this problem.

HB63A2

[HB63A2]

Thanks all for your comments and suggestions. To answer the question about the need to check the Fuel Pump Pressure, it goes back to carburetor problems. After the car sat for about a month I went to start it and it started right up, but would not run without my foot on the gas pedal, even after it was up to operating temperature. I took my foot off the gas and it stumbled and died. I got out and was surprised to see that the carburetor leaked a significant amount of gas (luckily no fire)! I took the bonnet off the top of the carburetor and the secondary butterflies were wet. I could see a residue of gas around the Air Horn Gasket in-between the Air Horn Assembly and the bottom part of the carburetor as well as around the accelerator pump.

People suggested that it might be debris in the inlet needle valve, inlet valve that has a hardened tip, a stuck or sunk secondary float. I described my problem to a person that rebuilds carburetors and the amount of fuel that suddenly leaked out. In addition to the other comments, he questioned if the fuel pump pressure was too high. The fuel pump had been replaced with the correct one for a supercharged Avanti just before I bought the car about four years ago. He said he had worked on other cars recently with fuel spillage and seepage similar to mine and tested the fuel pumps to find that they had excessive pressure (over 6 lbs.). He surmised that recent rebuilt fuel pumps are just junk and suggested testing the fuel pump pressure before tearing into the carburetor.

Have any of you had excessive fuel pump pressure problems with your Carter AFB carburetors with superchargers? I’d hate to tear down the carburetor if the real problem was the fuel pump!

Thanks in advance for any comments or suggestions to solve this problem.

HB63A2

[Ross]

Rest assured that the pressure from your 4 year-old fuel pump did not suddenly increase on its own. That is determined by the spring inside pushing on the diaphragm and springs do not get stronger with age. I would certainly go with the needle valve theory or a float sticking to the bottom of the bowl after the gas evaporated away. In which case give the carb a little tap with a hammer and try again. Have seen this problem many times with cars coming out of storage, but usually after a longer time.

[Dan Timberlake]

Checking fuel pressure ( and delivered volume) is a wonderfully accurate and useful method of determining the mechanical health of the entire fuel system from the fuel tank, through all the fuel lines and filters and pump(s). No amount of parts changing can realistically be expected to achieve that.


“When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.”
Lord Byron

[IMJ]

Since the R2 AFB is a sealed unit and you noticed fuel leakage around the accelerator pump might the seal there have failed ? Maybe the boost from the blower is pushing the fuel out in that area. As others have stated, the fuel pump wouldn't increase pressure output after being in service for 4 years. I suppose the fuel pressure might increase if the return line to the gas tank became restricted, but I don't know for sure. As for the gauge holding pressure for 1-2 minutes after the engine is shut off as stated in the fuel pressure tester manual, I believe they are referring to an injected system with the fuel pump in the gas tank.

[bezhawk]

The needle tips get hard with the alcohol in todays gas formulations. It happens over time. If the top seal fails on the fuel pump, then it fills with oil from the engine, and since oil is less compressible than air, it increases the fuel pressure just like adds spring pressure, or supercharger boost does.