I’m using an Autolite 4100 on my 67 Mustang coupe with a 302 engine and mild 268 cam. I can’t get enough idle rpms to run without cranking on the idle stop screw and getting into the transition circuit of the carburetor that makes the idle mixture screws useless. I’ve got the initial timing set to 13 degrees. I don’t know what the correct fix for this would be. Any help would be appreciated
Need tuning help with 4100 Carburetor
- Thread starter Gary’s 67
- Start date
Blackhawkxx
Advanced Member
- Mar 3, 2023
- 496
- 490
- 73
Try this if it applies, if you have vacuum advance on the dist. and is connected to ported vacuum, move it to manifold vacuum. It will increase idle rpm. If you get pinging while driving, you can adjust from there.
Woodchuck's 4100 idle mixture adjustment 101.....
1. Turn each mixture adjustment screw in until VERY LIGHTLY seated.
2. Turn each mixture adjustment screw out exactly 1-1/2 turns.
3. Connect vacuum gauge to intake manifold source (preferably a tee on the PCV hose). DO NOT use a vacuum source tapped into an individual intake runner! If no vacuum gauge is available, connect a tachometer as directed by the instrument's manufacturer.
4. Turn each screw, alternately and no more than 1/4 turn at a time, in whichever direction results in an immediate increase in manifold vacuum and/or rpm.
5. Continue turning in that direction, while maintaining curb idle speed as close to specification as possible, until vacuum and/or idle speed begins to decrease.
6. Return to the last "good" setting.
7. If you have to have more than 1/4 turn difference between the individual mixture screws you have other issues that need to be corrected.
PS: Don't forget about the Secondary Idle Adjustment, which must be made with the carburetor off as it faces up from the base of the carburetor.
https://www.carburetor-parts.com/assets/manuals/autolite_4100_manual.pdf
1. Turn each mixture adjustment screw in until VERY LIGHTLY seated.
2. Turn each mixture adjustment screw out exactly 1-1/2 turns.
3. Connect vacuum gauge to intake manifold source (preferably a tee on the PCV hose). DO NOT use a vacuum source tapped into an individual intake runner! If no vacuum gauge is available, connect a tachometer as directed by the instrument's manufacturer.
4. Turn each screw, alternately and no more than 1/4 turn at a time, in whichever direction results in an immediate increase in manifold vacuum and/or rpm.
5. Continue turning in that direction, while maintaining curb idle speed as close to specification as possible, until vacuum and/or idle speed begins to decrease.
6. Return to the last "good" setting.
7. If you have to have more than 1/4 turn difference between the individual mixture screws you have other issues that need to be corrected.
PS: Don't forget about the Secondary Idle Adjustment, which must be made with the carburetor off as it faces up from the base of the carburetor.
https://www.carburetor-parts.com/assets/manuals/autolite_4100_manual.pdf
Similar threads
