Adjustment of 40DFi air bleed
Adjustment of 40DFi air bleed
What are some of the methods used to adjust the air bleed screws on the base of the 40DFi/2 carbs?
Re: Adjustment of 40DFi air bleed
Hi Jimmy,
There's an old thread that provides a clue. It's called "Carb Synching" and pops up immediately if you search those words. There's also one called "Carb Synching (the sequel)" The first (and maybe the second) was started by John Vardanian. In that first thread somewhere, I described very roughly how I synchronized the air bleeds by resetting my sector gears first to compensate for forty years of aluminum sector gear wear. There are also lots of documentation mentioned, including some 40 DFI (all sorts) Weber spec sheets that I got from a VP of Weber Italy. I still have cleaned-up electronic versions of them and can send them if you think they would be helpful.
Resetting the sector gears, with the carbs off the engine, is important to 1) accommodate the gear wear and 2) reset and synch the two plates relative to the slots in the bore that transition between the idle circuit and the main circuit. Otherwise, there will be unequal fuel flow side-to-side during the initial throttle opening, and perhaps erratic flow side to side even at idle. Resetting the sector gears is not difficult but it's complicated. It takes a lot of manual dexterity and finesse. On my Queen (40DFI/5 carbs), it was worth it. The biggest problem is visualizing which direction to bias the plates to take up the gear lash and get both plates completely closed in the bores and then have them start to crack open at exactly the same time. The throttle lever opens one plate and that plate opens the other through the sector gear.
Once the plates are synched at closed bore position, presetting idle speed a couple of turns, the carbs go back on the engine. Then synchronizing each carburetor left to right with the air bypass screws and my synchronizer was a piece of cake (or panettone). Finally, I synchronized carb-to-carb like we always do, but this time, it was easier and the results were that it started, idled and ran like a new car.
I suspect that it's only necessary to reset the air bypass screws on an old carburetor with worn sector gears - which all of ours are. The primary effect of worn sector gears are difficulty in setting a smooth idle (because of the side-to-side differences), and in the off-idle transition (due to differences in left-to-right transition air-fuel ratio).
Let me know if you want the Weber Spec Sheets. They are very instructional for setting float levels and setting up the carbs on a workbench (not a flow bench). They also have exploded views and parts lists.
Tom Kizer
There's an old thread that provides a clue. It's called "Carb Synching" and pops up immediately if you search those words. There's also one called "Carb Synching (the sequel)" The first (and maybe the second) was started by John Vardanian. In that first thread somewhere, I described very roughly how I synchronized the air bleeds by resetting my sector gears first to compensate for forty years of aluminum sector gear wear. There are also lots of documentation mentioned, including some 40 DFI (all sorts) Weber spec sheets that I got from a VP of Weber Italy. I still have cleaned-up electronic versions of them and can send them if you think they would be helpful.
Resetting the sector gears, with the carbs off the engine, is important to 1) accommodate the gear wear and 2) reset and synch the two plates relative to the slots in the bore that transition between the idle circuit and the main circuit. Otherwise, there will be unequal fuel flow side-to-side during the initial throttle opening, and perhaps erratic flow side to side even at idle. Resetting the sector gears is not difficult but it's complicated. It takes a lot of manual dexterity and finesse. On my Queen (40DFI/5 carbs), it was worth it. The biggest problem is visualizing which direction to bias the plates to take up the gear lash and get both plates completely closed in the bores and then have them start to crack open at exactly the same time. The throttle lever opens one plate and that plate opens the other through the sector gear.
Once the plates are synched at closed bore position, presetting idle speed a couple of turns, the carbs go back on the engine. Then synchronizing each carburetor left to right with the air bypass screws and my synchronizer was a piece of cake (or panettone). Finally, I synchronized carb-to-carb like we always do, but this time, it was easier and the results were that it started, idled and ran like a new car.
I suspect that it's only necessary to reset the air bypass screws on an old carburetor with worn sector gears - which all of ours are. The primary effect of worn sector gears are difficulty in setting a smooth idle (because of the side-to-side differences), and in the off-idle transition (due to differences in left-to-right transition air-fuel ratio).
Let me know if you want the Weber Spec Sheets. They are very instructional for setting float levels and setting up the carbs on a workbench (not a flow bench). They also have exploded views and parts lists.
Tom Kizer
So many sidewalk cafés - so little time left.
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
Re: Adjustment of 40DFi air bleed
Tom, thanks for the search info, Dykes details are right on , as usual, and will work fine. Jim