dual capacity accelerator pump-how can I tell if it's working corrctly

[KaptKane]

Greetings!  Newbie here!
I have an 85 Suburban 350 with original Quadrajet.
The truck is now running very rich (tailpipes black) and the fuel mileage has gone from poor to terrible!
I checked my coolant temp and it is 190.
How can I make sure my electronic accelerator pump is operating correctly?  How can I improve my fuel mileage!
Thanks in advance for your help and consideration.

[Cliff Ruggles]

The accl pump bypass system has NOTHING to do with running rich and horrible fuel economy. 

They built millions of Q-jets w/o that system, and it was a lame attempt to decrease accl pump shot on a hot engine to further improve fuel economy on very late truck engines. 

Problem is the accl pump only works with quick throttle movements, and does nothing for steady throttle driving city or highway, so really not a player in the carb running rich and the engine using a lot of fuel.

I would call the shop and order one of our rebuild kits to get the carb completely/correctly rebuilt with good parts.  This will restore it to correct specs and back to getting good fuel economy again......Cliff

[429bbf]

you asked a very broad question with a lot of details left out , does it have a catalytic converter i don't know if they were installed on that vehicle . if so could be plugged . is it firing on all 8 cylinders, hows the distributer,if it has a lot of miles the timing chain could be worn out , some of them had cam issues,don't blame the carb till you have investigated lots of other things . I've seen old chevys with gas running out the throttle shafts they were so worn out and still ran like a champ once you got them fired up . try narrow this down a little bit and you may find a different problem ,etc spark plug wires ,spark plugs if there good don't change them just things to look at .fwiw