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Carter BBS Carburetor Vacuum Advance

Carter BBS Carburetor

Hi Mike, I recently purchased a 1966 Plymouth Valiant Signet with a 225 /6. It has a Carter 6-1695 B&B 1bbl on it. There is no tag on it unfortunately. You’ll find 4 pictures of it that I sent along with this email. The port on the passengers side of the Carb is for the vacuum advance. This port should be ported but it always has vacuum even at idle. Idle is at 600 to 700 rpm. I even dropped it lower to see if the idle was to high, but I still have constant vacuum at that port. Would you know why this is? The way it is now is the distributor is always at full advanced even at idle. Would there be something missing inside the Carb that you know should be there? Anything I can check? Other than that the engine runs great.

Some engines, starting in the 60’s, had full vacuum to the distributor.
Ported vacuum signal for the distributor advance came from above the throttle plate at idle. As the engine speed was increased, incoming air rushed by the now open port and created a vacuum signal. This signal would advance the timing 8 to 12 degrees. Starting in the mid to late 60’s some manufacturers modified the distributor curve and camshaft to create less emissions and along with these modifications came the full vacuum signal to the advance?! He needs to research his application to determine if it needs a full or ported vacuum signal. If ported is required, then he may have the wrong carburetor. I can install a ported circuit in most carbs by drilling a small circuit above the throttle plate (he can also) about 1/8″ above the plate at idle position.

Updated on 12/06/2020

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