Very frustrating carb problem

[Tyler]

Hey everyone...

I'm having a really tough problem with my '83 Silverado 305 4bbl:

I've owned the truck about 5 months, and I've had a rough idle the entire time. I rebuilt the original carb, rebuild another carb and finally bought a new one, all with no improvement.

The truck has always smelled rich, or at least a really heavy exhaust smell. It will run better with the choke on than it does with it off, and now has gotten to the point that it won't really idle. If it dies, you have to pump the gas a couple times to make it catch again.

I have adjusted and adjusted the idle mixture, and the richer you go with it, the more stable the idle, although it still wavers up and down.

Anything off idle, it runs very well, doesn't pop or backfire or anything of the sort, just a horrible idle.

I've adjusted the timing up and down, made no real difference. I checked the egr valve and it was fine.I re-did all the vacuum lines and even started plugging the carb ports to try to make it change, it didnt.

At this point I'm starting to consider mechanical issues although the engine seems to be sound..it only has a little over 100,000 miles on it.

Timing really out of whack? Blown head gasket or intake gasket? Can a fuel pump screw up and start pumping with way too much pressure?

It acts to me like it has a massive vacuum leak, but where?? ive searched and searched.

I appreciate any advice...