My first challenge after reinstalling the Quadrajet in November 2016 was hard starting in cold weather. After much trial and error with choke adjustments and APT adjustments, I learned that both have a great effect on cold starts. If the part-throttle fuel mixture is nowhere close to being in the ballpark, no matter how rich the choke is set, the fuel mixture mixture will be too lean until the intake manifold is fully warm and will therefore require much gas-pedal pumping during warm-up.
While I was driving the car in 2017 to get my APT setting right, I found that I had a persistent lean cruise and eventually reached point where I had the APT turned out 6 turns. That left very little travel in the metering rods. While taking the car out for ride in May 17, my car suddenly started having a poor idle and subsequent drives became worse. It felt like I had an intermittent severe vacuum leak, which made the car a bear to drive in heavy traffic. After some troubleshooting, I noticed that only my left (choke side) primary venturi was flowing any fuel and the right-side venturi was completely dry. After taking the carburetor apart twice on July 3 and blowing out the passages with carburetor cleaner did I once again have a smooth idle.
Another challenge I discovered was with carb idle and ignition timing. The OEM specifications for my engine are:
- idle speed 550 RPM in Neutral
- ignition timing: 2.5° BTDC @ 550 RPM
- distributor PN 2444648 (distributor: 12° @ 2200 RPM centrifugal & 7° @ 13" Hg vacuum)
The commonly recommended performance timing for my car is:
- total mechanical timing (initial + centrifugal) 30-32° BTDC, all in by ~3000 RPM
- total advance (mechanical + vacuum): 45-50° BTDC (leaner part-throttle mixtures require more advance)
By advancing my initial timing from 5° to 8° BTDC, the advance curve in my DC distributor (P3690788) provided the recommended advance (distributor: 11° @ 800-1200 RPM centrifugal w/ single red spring & 7° vacuum). However, advancing the initial timing also increased my idle speed and I could only reduce it back down to ~600 RPM in Drive with the throttle completely closed. Without recurving my distributor, an additional 2° of initial timing would cause my idle speed to be even higher. I got the distributor through Mopar Performance (formerly Direct Connection) and it was used for performance (drag racing). For better highway fuel economy, I would still need a bit more vacuum advance.