Under the black choke cap is where most of the action will take place. The bi-metal spring will engage the choke when no electricity is flowing through it (cold). When you hit the key, 12-volts starts heating the spring and opening the choke plate. It's important to note that when installing the choke cap, be sure the bi-metal pick-up lever (in the housing) fits into the loop on the bi-metal spring. We checked this by turning the choke cap in both directions. The choke plate opened when rotated clockwise and closed when rotated counter clockwise.