1953 cadillac series 62 fuel pump

[MIKE2CADDIES]

Fuel pump filling up most of way, but not to the top, and has air bubbles and the fuel filter bowl is not filling at all. Car is running but carburetor is starving for gas. When electric fuel pump is turned on it improves the situation initially but not 100% and eventually stops making a difference. The tank and all gas lines have been replaced. The mechanical fuel pump has been rebuilt and rechecked as well as the carburetor. The fuel pump has been modified, by builder, since the wipers and antenna are no longer vacuum. The fuel is not boiling it is air  bubbles. We ran gas directly into mechanical pump from bottle and problem still exists. No time for gas to heat up and gas lines are cool to the touch. We have had it running with mechanical pump full, with no bubbles, and the filter bowl full for extended time but never lasts.
1- Is the mechanical fuel pump supposed to be 100% full with no air bubbles and is the glass filter supposed to be full as well?

2- Any ideas how to remedy this situation?

3- I know there isa difference between 52 and 53 carburetor and trying to get eh correct serial numbers for 53 to verify mine is correct.

Thanks

[P W Allen CLC# 20193]

Hi Mike. Actually, there are two different fuel pumps that were used on the 53's. The early run cars used the pump with the glass bowl on top and later in the model run they switched to the one without the glass bowl. A separate glass bowl filter was supplied when the switch was made. For some reason I could never understand, they mounted this filter upside down just as it was on the older pumps. I turned mine around so the bowl is more easily emptied of any sediment without spilling it all over the place. Anyhow, I can tell you that my car does the same as yours. Sometimes the bowl is almost full (never has been completely full), sometimes half full, sometimes empty. and like you, I see some bubbles from time to time. However, on my car, I have no gas starvation problems at all, no matter what the level is in the bowl. I fretted over it for a while but eventually just accepted it. I've really had no trouble with it. From your description, it sounds like you are running the fuel pump with the glass bowl on top AND a separate glass bowl filter? If yes, this could be a problem. It is my understanding that a separate glass bowl filter was used only when the newer fuel pump without the glass top was installed. I've attached a few photos showing my car with and without the glass top fuel pump. Note the gas level in the pic of the glass bowl filter. This pretty much the norm on my car.

[MIKE2CADDIES]

Thanks, I am going to pass this on to my mechanic. One thing that I want to add is that the bubbling is fairly constant and it is very strong. It looks like boiling but it is not. I can see the bubbles come from the metal opening in the fuel the pump and the entire perimeter of the bottom.

[P W Allen CLC# 20193]

Mike, Strong bubbling usually indicates an air leak someplace in the suction line from the tank to the pump. I know you said that everything is new, but worth a check. The thing is that you can have an air leak in the line someplace, but they won't leak any gas out. Makes them tough to find. You also say the fuel pump has been modified because you don't use the vacuum wipers. I don't know what modification was made, but bubbles at the fuel pump is not normal. Actually, if your not running vacuum wipers, you can use a single stage pump that has no vacuum pump built into it at all.

[m-mman]

Vacuum check your line. Discussion that might be of assistance:
http://forums.cadillaclasalleclub.org/index.php?topic=143905.0

You absolutely must perform BOTH a pressure test and a flow test on your fuel delivery system.

1. fill carb with fuel - a squeeze bottle that squirts into the vent pipe will fill the bowl. When the bowl is full the car SHOULD run/idle for 3-4 minutes without any fuel pump activity. If it wont run with a full carb, then the fuel pump aint your problem.

2. Attach a (good old fashioned) fuel pressure gauge to the line that leads from the pump to the carb. Crank engine, have it start. Watch to see how much pressure the pump delivers to the carb. 5-8 psi should be OK. (modern FI fuel press gauges wont read this low)

3. Disconnect fuel line at carb and use hose to direct into a 'bucket'. Watch to see how much FLOW comes from line. It should deliver a good strong gush of fuel. 'Spitting' is no good. The gush should happen with each cycle of the pump.
There are specs that show exactly how much fuel (ounces) the pump should deliver in how many seconds/minutes but if you see a good strong gush/flow it is good.

No, glass bowl filters do not operate 'completely full'. Neither do transparent in-line filters but I have never understood why or where the air is coming from, or why sometimes the bowl is fuller than at other times.

[MIKE2CADDIES]

Thanks , I am going to pass this on to the mechanic