1938 Cadillac Mechanical Fuel Pump

[cadillac60]

Because of on going problems with my fuel delivery I have put a test on the mechanical fuel pump. The specifications state it should be 3 to 4 1/2 PSI.  At idle the test gauge goes up to 5PSI I also tested at a higher RPM & the test still shows 5PSI. It takes 1 Min 35 seconds to drop to zero once I turn the engine off.  Is this unusual that the Fuel pump tests higher than the specification? Does this indicate that something may be wrong with the pump?  Or would the 1/2 PSI over the spec make any difference?

Bruce

tralee@telus.net

[John Washburn CLC 1067 Sadly deceased.]

Bruce,

I am no expert on these fuel pumps, but first question is are you using the original 1937-1938 fuel pump? This one has the metal protrusion on top. These were replaced by the factory with the later models that allegedly reduced the chance of vapor lock?

Now with the viton tips used on the needles in the kits now available the chance of overpowering the needle with an extra 1/4 to 1/2 psi is negligible (my opinion). So I would not worry about this extra pressure which should help reduce the probability of vapor lock.

If you are still worried you can add a fuel regulator between the pump and the carburetor.

Finally, the residue pressure is not a problem.

John Washburn

[cadillac60]

John, Thank you for your reply, The fuel pump I have is with the glass fuel filter on top, so I guess this is the one you mentioned the factory replaced to stop the vapour lock. I may look at putting a regulator between the fuel pump & the carb. The main reason for this is I purchased a 6V carter electric fuel pump & after been told it  would be set at less than 5 PSI & should work fine for my car. I find out much later that in fact it is set at 5 3/4 PSI & if used for anything else than starting the car after sitting for a while it does flood the carb. I just had the carb (AVV26-)-(original AVV25) completly overhauled. I noticed when I took the plug out of the side of the carb to check the level of the fuel in the carb that it was well below the bottom of the threads where the plug fits in. According to the manual it should be up to the bottom of the threads.  How important is this to have it right on?

Regards

Bruce

[John Washburn CLC 1067 Sadly deceased.]

Bruce,

You really want to the float levels to be correct. So if the gas level is low can indicate a bad adjustment.

I am confused about the electric fuel pump issue. If you leave the pump on, with the car running, the carburetor pushes to much gas out and stalls the car? Let me know the exact symptoms somthing ain't right in Denmark.

Finally, and i can't help myself, it is AAV26 and the original is a AAV25. You had to many V's and not enough A's.

The Johnny

[cadillac60]

jOHN

On a long trip back in May I was forced to use the electric fuel pump as I was having trouble with the mechanical pump cutting out & starving for fuel. I was OKh with the electric pump until I was going down a hill and coasting or stopping for a short period of time, then the electric pump would load up the carb. I could feel the car starting to stall so I would turn off the electric pump & go back to the Mechanical pump. I had to go back & forth between the 2 pumps to get home. It wasn't that hot out so I am not sure if the mechanical pump was vapouir locking or I had other problems. I was about to take the mechanical fuel pump out & order a kit for it, but after putting pressure test on it & finding it was at 5PSI I am not sure why the mechanical pump is giving me these problems.  (I didn't think that the AVV looked right & I was to lazy to look it up!)

Thanks for your interest

Bruce