How to Tune Weber IDF Carburetor
1. Begin by insuring that for initial carburetor set up all the air by-pass screws should be in closed position. These are not normally used in standard carburetor adjustment. Note to do this, loosen the pinch nut, then turn the screw all the way in until seated, then re-secure the pinch nut.
2. Set the idle speed screw at ¼ to ½ turn in after contact with throttle lever. When doing multiple carburetors all linkage should be disconnected. All carbs should be bench adjusted to same setting.
3. Set the idle mixture screw to one turn out form lightly seated. When checking the seated position to make only light contact with seat, aggressive seating will damage needle and seat of carburetor,
Adjustment if possible should be to find smoothest idle with each mixture screw on all carburetors. Some prefer to do one barrel of each carburetor then come back and do the second barrel
4. Start engine as long as engine starts and runs do not turn up idle speed first.
5. After preliminary lean best setting of idle. Check carburetors for synchronization. Commonly done by checking lead or front barrel of each carburetor.
6. You will always want to bring high flow carburetor down to match the low flow carburetor. If this cannot be done you will need to recheck bench assembly for binding throttle in high flow carb. Once you have matched both carburetors you will need to set the idle to the desired idle speed setting. This will be done by adjusting both carbs up or down the same amount and re checking for synchronization.
7. Make one last check of lean best (smoothest running position) idle on all mixture screws one last time.
8. Best idle should end up with the mixture screws at or near one turn off seat. Check rule of thumb for idle jet selection on the other side of this page.