Fuel System: Low fuel pressure to the Carb?

[Bullet]

My 64 Cruiser (289), still needing a re-build, runs just perfect at idle. However, if trying to apply any power to the car, the engine stumbles and has no power. A mechanic said that I only have about 1 lb of pressure at the carb. He also said that I have a lot of air in the line. I have not replaced the gas line rubber hose along the front of the cross member to the fuel pump. I have replaced the rubber hoses by the inline fuel filter. Other than these two areas and potential the gas line, what else could be the culprit? I replaced the fuel pump 2 years ago, so would be surprised that it has failed already.

Also, I am not sure what generates the fuel pressure, am assuming it is the fuel pump pulling the gas from the tank. Any thoughts appreciated.

Mark

[BobPalma]

Don't be surprised if a new, original-type fuel pump has failed in two years. There's a reason Auto Zone conventional pumps, for example, now have only one-year warranties.

That said, there should not be a rubber fuel line under the engine on the front crossmember. Put a steel one in there.

Also remove the fuel line at the pump, the line from the tank. Use low air pressure to blow backwards into that line, toward the tank. While pressure is being applied (this takes two people), carefully follow the fuel line all the way back to the tank, looking for pinhole leaks, especially where the line is secured to the chassis with clips and fasteners.

Pinholes of rust can create leaks that aren't noticed because the line is under suction, not pressure, when the engine is running. However, those pinholes will allow the pump to pull some air along with the fuel, which could cause all the trouble you're having, Mark. BP

[jclary]

Well, for our older "Non-fuel injected" vehicles, using carburetors..."Pressure" from the pump is not as important as volume. Of course, in the case of a carburetor, pressure and volume are related. It takes enough pressure to supply sufficient volume to keep the carburetor bowl/reservoir supplied with enough fuel. However, downstream from the bowl, "pressure" is not the issue as much as metering rods, jets, venturi, and the interplay of negative airflow as the fuel is sucked and atomized into the cylinders.

Air in your gas to the carburetor would mean that there is a loose fitting, pin hole in a hose, or failing diaphragm. However, if air can get in, it would be reasonable to have gas leaking out. If you check all this out and find no problems, I suggest you check to make sure your points have not worn on the distributor cam and closed the gap a bit. They can be gapped too close and that will cause a big fall-off in power. Also, make sure the vacuum advance diaphragm is working properly. If not, you can have a smooth idle but poor power on acceleration.

These are simple checks you can make. My carb comments may be a bit too simplistic. There are other posters here much more qualified than me on the subject. Some of these carburetors have a little screen wire type filter right at the fitting where the fuel line connects to the inlet of the carb. (And some don't) Don't forget to check. I have had these little neglected screens to catch enough debris to starve fuel flow and cause the symptoms you describe. It is simple to use compressed air, blow them clean, re-install and you are good for another 50 years.

(Just came back to "edit" my post to acknowledge that Mr. Palma had apparently posted some very good suggestions while I was busy typing my reply. Anything in my post that conflicts with his...follow Bob's suggestion first. Then...if it don't work...blame him.)

[Warren Webb]

Along the line of what Bob said I would block off the line at the gas tank, then apply a constant air pressure to the line @ the fuel pump inlet hose. Spray the steel line with a soapy water solution & look for bubbles. No bubbles no leak.

Now on to what John said. In the shop manual you'll find them asking to test for volume. Disconnect the line at the carb running it into a container. Start the engine & see how much time elapses before the carb runs out of fuel. Measure the amount /time involved. It should come close to what the manual says.

[skyway]

FYI, the (original?) fuel pump that was on my 64 Cruiser when I bought it in 1980,
had a paper filter inside the tin housing on the bottom of the pump. After a couple of years mine developed the same symptoms as yours, and replacing that internal filter fixed it.

[Bullet]

Thanks guys! I will try these and report back.

Mark

[Pentax645]

If you buy a new fuel pump check the pressure output and compare it to the pressure your carb can handle. if the pump puts out more pressure than the float can hold back you will drive about a half mile before the car quits due to flooding. The auto parts stores sell fuel pressure regulators if your pump puts out too much pressure for the carb.

[Bullet]

I had some success today. I replaced the fuel filter and the car ran a little rough but started to settle down after a couple blocks. I decided to try driving it a little further and was making some right hand turns, not very fast, and the car would die. After the third turn, I could not get the car started again, so pushed it to the curb, luckily about 2 blocks form home. As I did, I noticed there was something dripping on the ground. So after I got the car out of the middle of the street, I looked and here was gas running (pouring) out of the old rubber hose next to the clamp I had just tightened. So I moved the clamp and re-tightened, and the leaking gas stopped, but when I went back to start the car, the battery was DOA. My son ultimately towed me home and tomorrow I go get new rubber fuel hoses and possibly a new battery. Always an adventure, but always fun.

Thanks for the tips, and so far I have not had to replace the fuel pump, but that may still need to be touched.

Mark