Fuel line empty overnite from fuel pump to carb

[femtnmax]

I notice the fuel line from mechanical pump to carb has no fuel in it after sitting overnite.  As if some amount of  fuel is draining back to the tank.  The car is indoors, no hot sun to cause vapor expansion/contraction.
Anyone else notice this?  Anyone using a one-way filter/valve in the fuel line to prevent backflow?
My first idea is check fuel tank vent, make sure its doing its job.

[Cooter]

Common problem thesedays with this sh*t turd fuel we are paying more for than the good stuff we were gettin just 10 short years ago. Alcohol (Corn Ethanol) evaporates twice as fast as fuel so crank the hell outta it and it will eventually fire up..Either that, or install an electric fuel pump to help prime the carb before cranking like the fuel injection cars do...

[72cudamaan]

Try clamping off the line just before the fuel pump. I don't believe that you could have that much fuel evaporate overnight.
Seems like the fuel pump should hold the fuel pressure overnight.    Maybe a bad diaphragm in the pump?

[femtnmax]

Seems like the fuel pump should hold the fuel pressure overnight.  Maybe a bad diaphragm in the pump?

I planned for evaporation...I have an electric pump for priming.  I ran the engine again today, then within minutes took the fuel line off...no fuel in the line.  The mechanical pump is a new Carter unit with less than 200 miles on it...guess new doesn't mean much any more. 

[ShelbyDogg]

I think that you are looking for fuel that you normally don't see. There are check valves in the pump.   Normally you jump in a car, pump the pedal once to prime the engine, then start the engine. The pump starts pumping right away.  You only need fuel up there right away when your bowls are leaking into the intake or the bowls boil away the fuel, which you already thought about.

If you want to see fuel and pump action, put in a temporary clear plastic fuel filter and watch it. They never fill all the way up and you can watch it for drainback.

I would not use a plastic filter permanently though, unless it was for my lawnmower.

[burdar]

Are all the factory vent lines hooked up properly?  Is the tank vented?  If you are pulling a vacume on the tank(due to not having a vent) you could be pulling fuel back out of the line when you shut the car off.

When you take the cap off, do you here a big rush of air enter the fill kneck?

[femtnmax]

Are all the factory vent lines hooked up properly?  Is the tank vented?  When you take the cap off, do you here a big rush of air enter the fill kneck?

Thanks for the ideas.
Had the vent lines hooked up correctly, no rush of air when filler cap removed.  I rechecked the fuel vapor separator and it did not flow as easily as I would have guessed...its the style with 4 hoses to the tank and a 5th hose fwd to the engine compartment.
So I cut the vapor separator in half, and tried to drill out the 5th line, the other 4 outlets had zero restriction.  Drilling ended up loosening a check valve within the 5th line.  Hosed it down good with carb spray, the valve rattles freely now...it flows better, but not totally free of restriction.   So welded it back together.  Had to coat the outside with JB weld to seal damp seepage.  On the outlet of the electric fuel pump I added a Moeller Marine anti siphon valve (has an internal spring loaded check ball).  Part number is 033802-10, and it fits the 3/8 NPT outlet of the pump.
All working well with no issues thus far.

[burdar]

The internal valve doesn't allow the vapors to pass all the time.  If you suck...then blow on the 5th tube, you'll hear the valve open and close.  It only allows air to pass through it in the middle of it's travel.  It's very possible that it was rusted closed.

Mine was rusted solid but I soaked the tank in EvapoRust and was able to get it working agin.  I'm glad it's working for you.