Q-Jet loses prime?

[slideways]

I had the truck running yesterday. There is zero fuel coming from the pump into the throat when pumping. The system is dry. Carter fuel pump M6626 is what i installed awhile back. I cant find any info about it having a check valve or not.

Will not having a filler neck and fuel cap on cause this to gravity bleed back into the tank? Is there some pressure retained in the system with a gas cap on?

[78 Chevyrado]

I found that unless it sits for 2+ weeks at a time, if having this problem it tends to be the fuel pump.  I had lots of problems with all different brands of the stock fuel pump even carters...  I ended up buying an edelbrock 1721 pump for mine even though its stock engine but it sits a lot.  In the two years since I installed it I haven't had that problem again.  I think the stock replacement pumps are being built to cheaply they let the fuel siphon back to the tank.  The last two I bought broke trying to tighten the fuel line up to it using a backing wrench and all.   IMO all stock replacement SBC fuel pumps are garbage. 

[MY1978]

Mine would do the same thing.  Even after sitting a day or 2 between starts, I had to feed it some juice down the carb to get it started.  When I had my sending unit replaced, I also replaced the 40+ year old hoses (filler and vent hose).  After having that done, starts like it should.  The hoses looked pretty bad after 40+ years.  Only thing I can figure is that maybe there was a crack that was causing vacuum to be lost, or maybe it was something to do with the sending unit.  Anyway, it worked.

[slideways]

Updating this, i bought and installed a cheap amazon check valve on the supply side back at the tank. The same thing still happens after a couple days. No fuel in the accelerator pump. The motor will fire up after about 20 seconds of cranking and run fine which means to me it literally has zero fuel in the supply line the whole way back to the tank or at least not enough to fill the bowl quickly to get a start. I figured the check valve would help this at least keep fuel in the hard line to the pump but apparently not. So my two next guesses are to buy an expensive fuel pump that will hopefully stop the backflow and/or i have never gotten confirmation that doing all of this with no filler/vent hose on the fill hole causes some type of atmospheric reaction to siphon fuel back. I'd have to mock up a hose and a cap on as i still dont have a bed on during the resto.

[JohnnyPopper]

Move the check valve to the rubber hose going INTO the fuel pump.

In theory, it will act like the check valve that is supposed to be in your pump.

Make sure you get the direction right, speaking from experience...