Q jet loses prime.

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CheemsK1500

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On top of a mid '80s 305, I have a mid '70s q jet With a divorced choke (the choke isn't hooked up at the moment.).

I have confirmed that the mechanical fuel pump works, but the truck won't start unless I dump gas in the carb first. Within a few hours everything in the carb leaks back into the tank, and I have to prime the carb again. Anything obvious I should check before attacking every fuel and vacuum line? Thanks.
 
fast 99

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Fuel inside the carb can't drain back into the tank. Sounds like the well plugs are leaking. Will require a rebuild and sealing the plugs. When apart lightly tap on the plugs, then seal with fingernail polish.
 

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CheemsK1500

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fast 99 said:
Fuel inside the carb can't drain back into the tank. Sounds like the well plugs are leaking. Will require a rebuild and sealing the plugs. When apart lightly tap on the plugs, then seal with fingernail polish.
Click to expand...
Upon further investigation, it looks like fuel is running leaking out right on the passenger side of the carb. Is this a result of a well plug leak or something else. My gasket is plenty tight....
 
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Picture? A well plug leak usually isn't visible. May be fuel is migrating out the throttle shaft?
 
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fast 99 said:
Picture? A well plug leak usually isn't visible. May be fuel is migrating out the throttle shaft?
Click to expand...
I drew a blue arrow pointing to the area where the fuel weeps sometimes.
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Throttle shaft seals and well plug repair in your future
 
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WZ7U said:
Throttle shaft seals and well plug repair in your future
Click to expand...

This is a remanufactured unit I picked up the other day, I'd like to think it isn't broken already. Have remanufactured carbs really gotten this bad in quality?
 
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They have always been [not just bad but] horrible. Wouldn't use a rebuilt unless the existing carb was missing parts or at one time had water inside. Usually took 2-3 to get a one that I could make work. Go back and get your core if it is rebuildable.
 
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Leaky well plugs were a problem on the earlier carbs from the 60's. G.M. changed the way they installed them and most of the problems went away. You can pull the carb add some fuel or spray carb cleaner and observe the well plugs to see if they leak.
I think well plugs a blamed too often.

Another problem is percolation, which is when the carb gets hot and the fuel boils out of the carb, all carbs do this if hot enough the problem with a Qjet is the fuel bowl is so small it will boil/evaporate dry. So during the summer extended cranking might be your norm. But it should start as soon as the fuel pump get some fuel to the carb.

If it wont start without adding fuel to the carb I would lean towards a bad check valve in the fuel pump or a pinhole in the fuel line from the tank.
 
CheemsK1500

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fast 99 said:
They have always been [not just bad but] horrible. Wouldn't use a rebuilt unless the existing carb was missing parts or at one time had water inside. Usually took 2-3 to get a one that I could make work. Go back and get your core if it is rebuildable.
Click to expand...
The unfortunate thing is that the carb before this one was a rebuild as well. I guess my choices are either keep playing the rebuild lottery, pay a premium for a quality rebuild, rebuild my current junk, or just buy a modern 4 barrel carburetor and all associated adapters.
 
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C10MixMaster said:
Leaky well plugs were a problem on the earlier carbs from the 60's. G.M. changed the way they installed them and most of the problems went away. You can pull the carb add some fuel or spray carb cleaner and observe the well plugs to see if they leak.
I think well plugs a blamed too often.

Another problem is percolation, which is when the carb gets hot and the fuel boils out of the carb, all carbs do this if hot enough the problem with a Qjet is the fuel bowl is so small it will boil/evaporate dry. So during the summer extended cranking might be your norm. But it should start as soon as the fuel pump get some fuel to the carb.

If it wont start without adding fuel to the carb I would lean towards a bad check valve in the fuel pump or a pinhole in the fuel line from the tank.
Click to expand...
When I disconnect the fuel line from the carb, and crank the engine, fuel shoots out. I think the carb is likely more at fault than the fuel delivery system. I won't rule out the possibility though, the rubber is certainly old enough to have developed a few cracks.
 
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Get a rebuild kit from Cliff Ruggles.
 
CheemsK1500

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I toyed with the idle/air adjustment, and now it seems to fire right up everytime. I think it was too lean the entire time. The idle seems kind of high now, but that might just be the nature of the beast.
 
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