'75 W200 won't idle
 

Hi all, the truck in question is a '75 5.9l W200 with a Holley 2 barrel carb. The truck sat all summer and the gas went bad in it, so I replaced all the gas and dissasembled the carb to clean it out (there was a lot of gunk in there). I had it running great for a while and then out of nowhere it stalled out. It will start (hard), but now it refuses to idle. If I rev it and hold the rpms up after a few seconds it will start to sputter and will stall if I don't pump the gas. The accelerator pump is working, and seems to be the only thing that will keep the truck running. Also, the float bowl is always full of gas when I take it apart.

To me it seems like the carb still has gunk in it and it's being starved for fuel. I've tried cleaning the carb three times with no change in performance. I've checked for vacuum leaks, can't find anything obvious.

So where do I go from here? Timing issue? Fuel filter? I'm at my wits end here guys, so any help is appreciated. Thanks!

does it only do this when you first start it or does it still doe it once you have hit operating temperature?

Only at operating temp.

does the choke seem to be working?

Yup, as far as I know anyway.

Could it be that the mechanical fuel pump is starting to fail?

Define "(there was a lot of gunk in there)". Where there any black flecks in the gunk? That is a sign of a fuel pump membrane failure.

No it was mostly varnish and some type of gel. If the fuel pump was on it's way out, it wouldn't run at higher rpms correct?

There are two ways a mechanical fuel pump normally fails. The diaphragm goes or the outlet valve fails. Without a fuel pressure test you can't say anything categorically about the pump being good or bad.

If you haven't replaced the fuel filter I would do that but it sounds to me, with what you have said, that your problem is still in the carb. You must verify the proper function of the choke. Guessing is not good enough. Anytime you try cleaning the fuel system by disassembly you can dislodge debris that can then clog the very smallest ports in the carb. It sounds like the carb is not flowing enough fuel thru the jets without support from the accelerator pump.

I agree, sounds more like carb trouble then fuel pump. When you cleaned it did you rebuild the carb?