True Vintage Tri-Power - Part 1: Behind The Scenes At SO-MO Speed Shop

A choke cable bracket assembly will be installed on the carburetor that the system type dictates. In this installation, the center carburetor has the bracket installed. Next, the air/fuel mixture screws are adjusted to a base setting.

The factory base gaskets are then placed on the manifold. Sealant is not required or recommended on the gaskets. The carburetors are then installed front to rear. The reason they are installed in this order is that the rear center stud nut can be hard to reach with a socket or crowfoot wrench once the next following carburetor is installed. The washers and nuts are put in place and torqued to approximately 15 ft-lb in a cross pattern at a progressive rate.

Next, the throttle linkage is installed. It may be installed as a pull or push type of system. Here they are installing the linkage in a pull-type action to avoid any clearance issues with a driver side throttle and transmission actuator cable (TV cable). The arms are installed from front to rear.

The torsion springs are utilized on the front and center link arms only. The rear link arm does not require a spring. The torsion spring is fit over the carburetor shaft. The hooked end goes around the link arm and the other end rests against the carburetor base. The link arms are set at approximately a 40-degree forward angle from the vertical. This should apply enough tension on the spring to snap the carburetor shut from the open position. Caution must be taken to not overtighten the screws. Once fully tightened, the torsion spring should keep the throttle shut against the stop screw on the opposite side of the carburetor.

The center carburetor arm is installed next in the same manner. It is placed at the same 40-degree angle as the other link arm. The torsion spring is set in the same manner as the front spring. For this installation the center carburetor arm is a custom-built piece from SO-MO. It has multiple adjustment holes for the actuator arm of the linkage, which allows a change in the linkage geometry for specific applications. This affects the rate at which the front and rear carburetors open in progression with the middle carburetor. This custom arm extends below the throttle shaft for connection of an automatic transmission kick down or (TV cable) cable. There is a pin with a button head screw to hold the cable slide arm in place.

Last, the rear carburetor link arm is installed as the other arms without a torsion spring, as it is not required. You can adjust the length of the rod that joins the front and rear carburetors to achieve the desired 40-degree angle on both link arms. Once this is attained, tighten the rod lock nuts against the spherical rod ends.

Now the secondary slide rod is put in place through the front and center carburetor link arm pins. It is extended about a 1/2 inch through the center link pin and the setscrew is tightened.

The link arms are adjusted on the carburetor throttle shafts until, when viewed from the top, the linkage rods are parallel with each other. Check that no parts are touching or could bind. The torsion springs should have enough tension on them to snap the throttles shut.