Early non APT primary rod set up.

[Pav8427]

Thinking ahead for a possible build. I have a clean 268 Pontiac carb in my pile. Other than making sure arms are level and straight, is there a start point to shoot for when setting primary metering rod height? Either a dimension or at least a good visual start point? Once in service, can or should you be able to tweek them lower/higher based on performance?

[Cliff Ruggles]

What is the carburetor part number?  Many end in 268?

[Pav8427]

Duh. Bet that would help a bit.
7029268

[Cliff Ruggles]

If you are using the original style metering rods there isn't much benefit from bending the hanger arms up or down to try to fine tune part throttle A/F.  Most important is to make sure the upper section is well located in the actual orifice of the jets, and that the tips are as well when the power piston is at full height. 

Pretty common for PP hanger arms to be bent, up, down, one up, one down, etc, from previous rebuilds.

I was working on a 1980 Caddy carb yesterday that was just rebuilt and both arms were bent down quite a bit.  It was pretty obvious just looking at the PP that they were not level, but it still was assembled that way by the previous builder.....

[mcx]

Those early Pontiacs don’t have any APT feature to adjust the primary rods depth in their jets …so purchase some washers and install one at a time inside the power piston and spring assembly…it will slightly lift the  primary rods just like a real APT screw…swap out your original primary rods for a set of “B” stamped rods…The “B” have a taper so they have a adjustment range to take advantage of. Only small disadvantage is you have to be careful removing the air lid each time to try an additional washer, though it’s pretty easy stuff on the early carbs.

[Pav8427]

Thats a new one on me. Would assume that would work for any non APT early units.
Will keep that one in my toolbox as I move forward.

Thanks. Doug