gas filter fills then empties

[petersspider]

I need your help! Up until yesterday my '74 spider has been running perfectly. While driving the car warm it suddenly felt like it had run out of gas. I pulled over and tried to start it and off we wnt...for about 300 yards. again and again. When I got home and investigated, i found that the clear glass gas filter would fill up and the car would start but would only use the gas in the filter and then stall out. I can hear the pump running fine but not after the car is started. Here are the symptoms...
-oil light comes on but still at 40 on the gauge.
-can hear fuel pump with key in pre-start position.
-can see the gas filter fill up.
-car starts and runs fine.
-can see the filter empty as car is running.
-I have put in a thick oil leak additive and it has worked on the leak. (100 miles ago)

Any ideas??? thanks for your help
petersspider

[So Cal Mark]

it sounds like the pump is only running when the starter is operating

[petersspider]

Thanks for your reply. The pump is running even before the starts is engaged. When the key is over as far as possible before turning the engine over, you can hear the pump and the gas filter filles up prior to starting the engine. Any ideas of a cure?
petersspider

[mbouse]

as i recall, the '74 used an electric fuel pump located in the trunk above the fuel tank.

getcher self a wiring diagram and trace the fuel pump circuit to ensure that what you have has not been altered by a previous owner, or damaged in some way. no breaks in the wires, no ground issues. Any chance that the vibrations of the car while the engine is running is causing an electrical connection to vibrate loose in this circuit?

[manoa matt]

It seams like the pump can no longer keep up with the fuel demand of the engine. After tracing the electricals and cleaning contacts, it may be a good idea to install a new filter, clean the small mesh screen at the gas inlet of the carb, and check the condition of the pickup screen in the tank. The carb float may need adjustment and replacement of the needle valve.
The pump could also be partially clogged giving less than optimal flow.

Start with the small stuff and do it systematically and eventually you will figure it out. Keep us posted.

[petersspider]

As it turns out, the oil sending unit on the side of the oil pump was defective. When I removed the electrical supply to the unit, the fuel pump started. This must be a safety feature to save the motor in the case of poor oil pressure. Once I removed and cleaned the unit and plugged the power back to it the oil light went off and the fuel pump worked fine. Who'd a thunk it!
Thanks for the help
petersspider