I have a 1985 K5 project I purchased a couple of months ago. I have done a lot of work to the engine to bring it back to commie-cali specs. The Blazer sat for about 4 years. To start with I rewired the engine compartment and cleared the rat nest. I have changed the plug wires, spark plugs, and distributor. I have changed all the temperature-sending units. I have replaced most of the vacuum hoses and made sure they are connected in the correct order and to the correct component. I have doubled checked my coil connection after reading several threads from forums about a loose or incorrect connection that can cause the stumble under load. The connection is good. The fuel pump was replaced in the last couple of years, and I rebuilt the Quadrajet carb. I HAVE TIMED AND RETIMED THE ENGINE (after some repairs like carb rebuild.)

The engine runs great at Idle, pops and spits out the carb with heavy acceleration. I used a vacuum gauge to tune carb and fine tune timing. I still have spitter and popping under load. I have noticed a gas smell and what I am guessing is fuel spray on the outside of carb after the carb coughs with acceleration.
WHAT AM I MISSING? redo the carb rebuild? I did notice the accelartion pump is only squirting one jet of fuel.

 

Any chance you could have an exhaust restriction, like a plugged catalytic converter? Does it have one of those gigantic pellet-style ones?

I would skip the "fine tuning" of the timing with the vacuum gauge and just stick to the factory spec, but that's probably not your problem.

 

Not sure about the Cat. it has been recently replaced, I can tell as it is not rusted and the welds look clean. That does not mean there is no restriction as the emission valve could be stuck. However, I would think that would cause an idle issue as well and I don't have that issue. I am running out of things (simple) to check I am getting down to internal issues like timing chains or valves. I have also read about the pick-up sock in fuel tank being an issue in the older Blazers.

 

Can you rev it up to high RPM with no load? If you can, and it's smooth, that would pretty much rule out anything like a broken valve spring. Sometimes, a worn exhaust lobe on the cam (something Chevy small blocks are notorious for) can cause backfiring through the intake, but it should also do it at high RPM in neutral, not just under load.

 

Yes, I can rev it up at idle. I do get an occasional sputter but it is after it stumbles and recovers. The majority of the time no issue at all while idling and with no load.
I did check my heat riser and sprayed some lubricant to sit overnight just to make sure it is working. I am back to doing a carb rebuild for a second time. I have even sprayed starter fluid looking for leaks and had no response from the engine when I sprayed the carb to the intake and all intake gasket areas.
I have even replaced the EGR valve which was stuck open. timing is about 6 degrees before TDC. Carb was tuned using a vacuum gauge.
Again the only irregularity I have is the accelerator pump only jets one stream when I throttle it and I am looking into the primaries.

 

It sounds like you have a clogged passage to the accelerator pump nozzle on one side (which I'm sure you already figured out on your own). I used to be pretty good with those carburetors, and I think I still have all the special tools, even. But it's been a LONG time since I've actually worked on one, and I'm lucky if I can remember what I had for breakfast nowadays, lol.

Sorry I don't have more to offer you, but please keep us updated with whatever you figure out.

 

Did you change the fuel filter again after repairs?

 

I replaced the carb with a reman Quadrajet. The engine runs great but still hesitates on load, and when i go WOT. I am leaning toward a tranny problem with my 700r4.