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Questions on Early Carter BB-1 Carburetor

Bill Jewell

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I have a 1930 Franklin model 145 that has a Carter BB-1 carburetor on it. I have a couple of questions about the carb:

How do I adjust it (which screws)?

It has an opening on the underside of the carb that I am not sure should actually open. It will sometimes leak gas from this opening. I have posted a few photos of it. Should something actually be in this opening?


Bill Jewell




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Your BB-1 is not one of the early ones, but one of the later ones.

There are three adjustment screws:

(1) idle mixture control (pointed brass screw secured by spring horizontally into throttle body)

(2) idle positioner screw (turning this screw rotates the throttle shaft)

(3) high speed or load adjustment (knurled screw horizontally into bowl)

Suggested initial adjustments:

Idle mixture control.....1 turn from lightly seated

Load ..... 2 1/2 turns from lightly seated

The hole in the air intake is to allow the escape of fuel when you shut off the engine. Make a "drip loop" from copper tubing, and run the other end to a vacuum source.


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