Anatomy of a Tri-Power Carb

Choke Tubes
The last items to add to this side of the tri-power are the choke tubes. There is a passage under the intake that allows exhaust gases to pass from side to side, and this super-hot air passing through the tubes is used to operate the choke and deliver warm air to the carb. The bottom of the tubes slip into two pressure-fit holes in the intake runner. Inside the choke housing is a spring that reacts to the heat, opening and closing the choke plate in the carb air horn. As the spring heats, the tension relaxes and the choke is pulled off. Hey, this was performance technology in 1965!

Throttle Linkage
Here's the business end of the tri-power. The throttle linkage assembly consists of a formed bracket that bolts to the butterfly shaft of the center carburetor. Attached to this bracket is the throttle cable from the firewall (not shown), the actuation rod going to the rear carb and the yellow throttle-return spring. As the cable pulls back the top of the bracket under acceleration, the rod is pushed rearward, activating that v-shaped rod on the other side and all three carbs start to open at the same rate. Stomping the accelerator pedal immediately opens all three at once, and then the fun begins. Most of these linkage pieces are available from the restoration aftermarket, as are the fitting and air cleaners.

Airhorn Sizes
From 1957 through '65 the Pontiac center carb had a smaller airhorn than the two outside units. Since they are basically funnels, the larger intake increases the overall cfm. For the last year of production, the '66 tri-power units had all three carbs open to the larger airhorns like the front and rear. This added a little more cfm and standardized parts such as the air cleaner bases and main body castings. If you're looking for a way to instantly differentiate between '65 and '66 center carbs, this is the quickest way of identification.