Carb looses prime after 24 hours. Keeps prime when fuel lines clamped.

[8point1]

Quadrajet # 17085213

1986 Chevy 1ton dually 2WD, automatic, stock 350 w/ 107k miles.  Was sitting for 3+ years.

-Looses prime after sitting for around 24 hours (so I assume fuel is not evaporating)
-Clamped both rubber lines from fuel tank, truck started a day later, then 2 days later
-Installed fuel filter with antidrain valve - no change

Do the mechanical pumps have a check valve?
Is it possible the fuel is siphoning out of the fuel bowl?
Do the well plugs leak on this late of model carb? (1986)
Do the rebuild kits (SR) come with instructions?

I have read other threads were Cliff has said this type of problem is either the well plugs or evaporation.  But I just can't get around it starting after I clamped the rubber lines.

Thanks.

[429bbf]

8 point1 .my exp. has been this .1 most pumps ive seen have a check valve. 2 .if you leave the little wire off the needle when you rebuilt it next to impossible to bleed back .3. ive only done 10  1980 and newer carbs none leaked .all the old ones leak bad.4.if your carb savy the instuctions are just fine.maybe the boss will chime in hes probably done 50,000 carbs and seen about anything possible.fwiw dean

[Cliff Ruggles]

Even if it drains back it can't symphon the entire bowl dry.  The fuel level goes down slightly, until the level of the seat in the carburetor.

Later castings can leak.  Our book describes how to high pressure test them and make repairs....Cliff

[8point1]

Thanks for the replies.

I went ahead and ordered a new fuel pump ($12.00 carter) and "the" book.

I am replacing the fuel lines as well and see what that does.  I'll update this thread.