The bigger orifice jet goes in the primary side.
Customer tip: A piece of paper towel folded over the screwdriver blade will hold the part, or a screw, until it gets started in the hole. (sometimes it helps to dampen the paper towel a bit)
The main metering system located in the primary side of the carburetor controls fuel flow between the low speed (idle) and power ranges. Its purpose is to provide efficient fuel metering during the cruising range of the automobile. Its operation is dependent upon air flow through the caburetor venturi which, in turn, creates a low pressure in the venturi, causing fuel to flow in the following manner.
At a point of sufficient throttle opening, the low pressure around the main venturi is multiplied many times in the boost venturi. This low pressure is transmitted to the tip of the main well tube or main discharge nozzle. Atmospheric pressure, which is greater, forces fuel from the float bowl through the main metering jets and into the main well. As fuel passes through the main well tunes, it is mixed with air from the main well air bleeds. The fuel mixture then passes from the tip of the discharge nozzle through the mixture passage to the boost venturi, and on into the intake manifold.
As the throttle opening is increased and more fuel is drawn through the main well tunes, the fuel in the main well drops. The calibrated holes in the main tubes are proprotionately exposed to the air in the upper well area. When this occurs, they become air bleeds mixing progressively more air with the fuel passing through the main well tubes. Although the nozzle suction is increased by increasing the throttle opening. The air/fuel mixture to the engine remains constant throughout the part throttle range. The calibrated main metering jet orifices plus the main well air bleeds provide the correct air/fuel mixture ratios for efficient combustion during the part throttle and cruising ranges.
Custom assortment (8 pairs, you choose the size)
Individual jets (you'll need to order 2 of each size)
