See Figures 1, 2, 3 and 4
Starting in 1973, all models use an electric choke to reduce exhaust emissions of carbon monoxide during warm-up. The system consists of a choke cap, a thermostatic spring, a bimetal sensing disc (switch) and a ceramic Positive Temperature Coefficient (PTC) heater.
The choke is powered from the center tap of the alternator, so that current is constantly applied to the temperature sensing disc. The system is grounded through the carburetor body. At temperatures below approximately 60°F (15°C), the switch is open and no current is supplied to the ceramic heater, thereby resulting in normal unassisted thermostatic spring choking action. When the temperature rises above about 60°F (15°C), the temperature sensing disc closes and current is supplied to the heater, which in turn, acts on the thermostatic spring. This causes the thermostatic spring to pull the choke plate(s) open within 1 1 / 2 minutes, which is sooner than it would open if non-assisted.
- Detach the electrical lead from the choke cap.
- Use a jumper lead to connect the terminal on the choke cap and the wire terminal, so that the electrical circuit is still completed.
- Start the engine.
- Hook up a test light between the connector on the choke lead and ground.
- The test light should glow. If it does not, current is not being supplied to the electrically assisted choke.
- Connect the test light between the terminal on the alternator and the terminal on the choke cap. If the light now glows, replace the lead, since it is not passing current to the choke assist.
- If the light still does not glow, the fault lies somewhere in the alternator. If the electrically assisted choke receives power but still does not appear to be functioning properly, reconnect the choke lead and proceed with the rest of the test.
- Tape the bulb end of the thermometer to the metallic portion of the choke housing.
- If the electrically assisted choke operates below 55°F (13°C), it is defective and must be replaced.
- Allow the engine to warm up to 80-100°F (27-38°C); at these temperatures the choke should operate for about 1 1 / 2 minutes.
- If it does not operate for this length of time, check the bimetallic spring to see if it is connected to the tang on the choke lever.
- If the spring is connected and the choke is not operating properly, replace the cap assembly.