What is this screw on Carter carb?

[70Bronco]

66 Belvedere II, 361, 2 barrel Carter carb.
Previous owner replaced the carb with a Carter BBD, 6-1887 stamped on top. Probably an updated version of the original. It’s similar to one in the original service manual. I noticed this adjusting screw on the back of the carb—does anybody know what it is? It’s not mentioned anywhere in the service manual.

 

[mopar 3 B]

You sure its an adjusting screw? It looks to be in the bowl area on the back side just about where the fuel level should be.
With out removing it or taking it apart who knows anyway I don't.

 

[70Bronco]

Definitely am adjusting screw.

 

[moparwacko]

"Idle Enrichment Adjusting Screw "
Early attempt at lowering emissions when on idle circuit. It predates the pulse duty solenoid on the BBD series. It only controls A/F ratio at idle, and never really worked well.......a LOT of BBD's were replaced because no-one really understood what it was and most were either all the way in/out after a rebuild and had a very messed up idle.
Haven't seen one in operation in years.
BTW, BBD's are one of the best most reliable carbs ever made.
Good luck!!

 

[70Bronco]

"Idle Enrichment Adjusting Screw "
Early attempt at lowering emissions when on idle circuit. It predates the pulse duty solenoid on the BBD series. It only controls A/F ratio at idle, and never really worked well.......a LOT of BBD's were replaced because no-one really understood what it was and most were either all the way in/out after a rebuild and had a very messed up idle.
Haven't seen one in operation in years.
BTW, BBD's are one of the best most reliable carbs ever made.
Good luck!!

Thanks! The carb was put on last year. It has the two A/F mixture screws on front.
Do you have any suggestions how to adjust that Idle Enrichment Screw, make sure it's adjusted properly, etc.?
Anything common areas you recommend checking on a BBD to ensure it's running at its best?

 

[moparwacko]

It looks to be a recent rebuild, so with that said.......
Standard carb setup:

• Make sure floats are set properly, needle & seat , etc.
• Set the main (front) screws at 1.5 turns from full seat.
• Set the idle enrichment (rear) at midpoint- full seat it, then remove, count turns until release.
• Ball & Ball carbs are super sensitive to any dirt - clean fuel and filter!
• When you remove the rear screw, spray carb cleaner in it. You'll be able to tell if passage is open.

The rest is regular carb playing, get your best vacuum reading adjusting the front screws. Then if the idle is still off, adjust the rear screw. All this helps if you have an A/F ratio gauge, but.......
Simple huh, enjoy!