See 1976 Chevrolet pickup with Rochester quadrajet upgrade on SBC 350 V8. We removed the hood, mounted a camera looking down on the air horn, and took it for a spin, running wide open on an uphill grade. See how the secondary air valve responds to rpm drop at each upshift of the THM. Also included is a smoking burnout.
New quadrajet set up
New air-gap manifold and custom/rebuilt q-jet. Sounds good but I still need to set the timing on the distributor and the carb is tuned already. Hope you like, nothing to fancy just a few revs and walk around...the Exhaust is true dual no x/h pipe and it has cherry bomb glasspacks(3 inch)
Rochester Quadrajet, the results!
Two mishaps, the first shown here, the choke coil I got was wound backwards, it made the choke butterfly wind up TIGHTER as the engine warmed up. I swapped on the one from the old carburetor fast enough, the second mishap made me feel like a crud and what did I mess up later that evening. The car would not start leaving the Etobicoke -Queensway show. It was not getting gas. We got it running by priming the carburetor, and boy, was I ticked at myself. In the end it was not my fault it looks like. The new accelerator pump umbrella and rod was a very poor and frail design, the umbrella came detached and stayed at the bottom of the of the pump well, and was a distressed mess. The maker will get a note from me. The upshot? The old assembly went in, all is perfectly fine, the slight tip-in hesitation is gone now too. Stupid lack of pride it seems these days making parts for even simple things like an old carburetor.
Identifying vacuum ports, late-style Quadrajet
I always see a lot of questions about what various vacuum ports do on a Quadrajet.
Here's a general guide that will point you in the right direction. Remember that there were many different Qjets over the years and vacuum port locations and number will vary. This video is representative of 1975-90 carbs.
More Quadrajet tuning, some things! Part two in this Saga Sept 13, 2010
With the camera sitting on the oil filler cap a few more things to show how a metering rod system works on a carburetor. The car has a slight stumble and surge at a light throttle cruise at about 55 to 60 MPH. By swapping out the .050 metering rods to .048 units, the stumble and driveability concerns are now gone. Going richer would mean worse fuel mileage one may think? No! Now that the mixture is right, LESS throttle opening is needed now, which means higher vacuum, and this way the metering rods will block off the correct amount of fuel, and in the proper timing and percentages, so the car runs much smoother. As stated many times, patience and reading up on, and understanding how these intricate carburetors work will help out very much! Enjoy!