The original Quadrajet for my 67 400 was in the trunk when i bought the car about four years ago in pretty rough shape. I've sent it off to two different quadrajet resto specialists (Quadrajet Pwr & Carolina Carb Specialists) and still encountering same problem that i'm looking for solution to. The carb is stumbling on the primary side upon initial acceleration. It hesitates upon normal acceleration and takes a second or two to 'catch-up'. Trying to determine if any one has experienced this issue and knows of a recommended fix..or if this a known issue these early gen quadrajets.
Check the fuel pump to make sure you get enough pressure and it's in good shape and not leaking. Check around the airhorn and entire carb to make sure you don't have any cracks. Ensure your vacuum hoses are connected properly and your timing is correct. Connect a vacuum gauge and and set the mixture screws to about 2 1/2 turns out from fully seated. Watch this video:
https://www.youtube.com/watch?v=HKGqKZsf3cc
Take a look at Cliff Ruggles site;
https://cliffshighperformance.com/simplemachinesforum/index.phpDo a search and then you can ask a question if you don't find what you are looking for.
I did a quick search and found a couple of posts with similar symptoms to yours and the recommendation was to open up or resize the down channel restrictors (DCR)
"Down Channel Restrictions are part of the idle circuit in the main body. The size of this orifice will restrict fuel flow during idle. When increasing compression and cam on an engine, these should be enlarged to allow more fuel to flow with less vacuum."
Does anyone have resources to figure out correct base plate part # for Quadrajets. Mine was swapped and i think some of the issues i'm encountering is because of that. Looking for correct base plate # for Quadrajet # 7027272 if anyone can help. Thanks all
Cliff rebuilt my QJ last winter.... got it back, it's like new, he hot tests/tunes it before he ships it back. Plug and play. He's the guru.
Sounds like you probably need to replace your accelerator pump ( in the carb). Take it off, and work on the bench... saves your back and wont drop little parts into scary places. Relatively easy fix, Cliff has the parts and can offer some tips.
(all this assumes you've got your timing correct and your idle mixture happy...)
I'm sure the right "whoever" can fix any carb but sometimes a carb just has gremlins. Maybe its got a manufacturing flaw? Who knows. My old Jeep never ran right. Had the carb rebuilt by a real reputable guy. Ran better but not the way it should. Finally I just bought a new carb. Ran great and never looked back. I'm also sure there are 10 people who will say that's bull and it just wasn't rebuilt correctly. Maybe so. But the new one saved me a lot of time and energy. In the end it cost about 2x as much as the full rebuild.
I also think most people just don't fine tune a carb correctly. I know I struggle. When I got my Bird, 2bbl, one of the screws was out 5 turns too far! I set it to factory and it ran terrible. Eventually we got it dialed in. More or less! Give me a lawnmower and i'll make it purr. Automobiles... ugh.
And as mentioned already you've got fuel filters, fuel pump, fuel lines, gas quality, timing and ignition system... etc that can all cause problems individually or several in combination. Heck maybe you got a bad spark plug or a bad wire?
check the vacuum. also do you have an electronic ignition? check the roter.