Gas draining back to tank

[Cracoliciadam]

I am new to the Fiat world and would like some help.
I have a 1979 Spider my brother and I are restoring, and we got it running after draining all gas and purging the lines. We drove it around for a good hour without fail, but after 3 days of sitting it’s bone dry. And it doesn’t crank/pump the gas up from the tank to get it running again.
Any suggestions?

[18Fiatsandcounting]

You have a carbureted version with an electric fuel pump, right? The reason I ask is that some (California) Fiats were fuel injected in 1979.

If you have an electric fuel pump, you should be able to turn the ignition on (but don't crank it) and hear the pump whirring away in the rear of the car. After 5 or 10 seconds, this should have pumped gas up to the carb, and it should start. If not, there are several possibilities:

1) the pump is only working intermittently.
2) the pump is partially plugged with sediment and such (pretty common)
3) The fuel line into the tank has a metal "sock" filter on the end of the pickup, and this is plugged
4) The flexible line between the fuel tank and the fuel pump has a small leak. Not enough to dump fuel out, but enough so that the fuel pump is pulling in mostly air.

If by some chance you have a mechanical fuel pump (on the engine), let us know.

-Bryan

[Cracoliciadam]

So sorry! I shouldve specified that, I have a mechanical fuel pump and not an electronic one.

[18Fiatsandcounting]

Ah, the plot thickens! This is not uncommon for mechanical fuel pumps, and what happens is that there is a very small (pinhole) hole in the diaphragm of the pump, or a very tiny leak in one of the hoses to or from the pump, and so the gas slowly drains back to the tank due to gravity. The solution is usually a new fuel pump and checking all the hoses and connections. Sometimes a one-way valve rated for fuel use inserted between the pump and the carb can help here, so check with your auto parts store to see if they have such a beast. 5/16" connections, if I recall.

However, there should be enough gas in the float bowl of your carb to be able to go several days without evaporating. If the gas is evaporating that quickly, then your float bowl is probably open to the atmosphere at some point (it shouldn't be). Check any hoses that lead from the float bowl cover to see if there are any leaks.

-Bryan

[Cracoliciadam]

Awesome, thanks for the help.
I’ll order a new pump and check the lines.
The car has sat for about two years, Im sure it’s in need of a pump.