When do you know a fuel pump is going south?

[tecton]

other day at an intersection, im stopped, awaiting a green light, i get it, hit the gas, truck doesnt move,

its stumbling really bad, pouring black smoke...it moves enough to get it off the road then dies...wont start for a while, finally i mash the pedal onto the floor and it starts and i rev it a few times and it seems ok, i continue on my trip without incident

is this the fuel pump/filter or just the carb?
im taking the k5 into the shop in the morning to get some PM done before winter, oil trans change, rotors, radiator leak, ect...stuff i would have done if i had a place to do it...should i be looking for a new pump/filter and adjust the AF on the carb while im there?

 

[Corey 78K5]

The way I was tought to test a Chevy mechanical fuel pump was to unhook the line going into the carb hold it out and have someone turn the engine over and if it shot over the finder you were good to go. Sounds crude but what the hell it works /forums/images/graemlins/tongue.gif
From what You say it almost sounds like You have a bad float and it'd getting flooded. I would say the float has a hole in it and is filling with gas.

 

[m j]

black smoke is too much fuel
careful of stuck floats I had a nasty engine fire due to one

 

[diesel4me]

Usually when a chevy mechanical fuel pump croaks,it stops pumpimg enough fuel to the carb to make it stall, or bog out on hills or heavy pulls--and they also often fill the crankcase with gasoline,and dilute the oil --not good for your bearings and other internal parts.I've seen engines ruined by this happenning--it loosens up a lot of dirt and sludge and sends it throughout the engine.I agree it sounds like a stuck or sunken float--the foam floats in a Q-jet should be changed at every overhaul,they can get soggy and sink,flooding the engine--brass floats are better,especially if you run any additives like dry gas,fuel system cleaner,etc.I'd fix your carb and change the oil as soon as possible.Sometimes when the diaphram fails in the fuel pump it will leak on the ground out the little "weep hole"in the casting--if its leaking there,you can bet its allowing gas into the crankcase too.In rare cases the diaphram may get too stiff with age and cause the pressure to get to high,and overwhelm the needle and seat valve and cause flooding too. /forums/images/graemlins/crazy.gif