[Kenth]

Carter 3898S is from a 1965 421 A/T engine.

NO 1965 Pontiac Carter AFB has a vacuum spark port. Spark passage is open to manifold vacuum.

For 1966-67 ONLY Carter AFB´s using A.I.R. uses a vacuum spark port. ALL other Carter AFB´s for 1966 Pontiac V8 uses full manifold vacuum to the ignition vacuum advance.

If you really need a regular non-A.I.R Pontiac Carter AFB with a vacuum spark port, look for a 1964 AFB, (except 3647S) and certain earlier units.

FWIW