The dwell angle is the number of degrees of distributor cam rotation through which the points remain closed (conducting electricity). Increasing the point gap decreases dwell, while decreasing the gap increases dwell.
The dwell angle may be checked with the distributor cap and rotor installed and the engine running, or with the cap and rotor removed and the engine cranking at starter speed. The meter gives a constant reading with the engine running. With the engine cranking, the meter will fluctuate between zero dwell and the maximum figure for that setting.
- Connect a meter as per the manufacturer's instructions (usually one lead to the distributor's terminal of the coil and the other lead to a ground). Zero the meter, if necessary.
- Check the dwell by either the cranking method, or by running the engine. If you are checking the dwell using the cranking method, do not operate the starter for more than 15 seconds at a time. Excessive cranking may cause starter damage. If the setting is not correct, the points must be adjusted.
- To change the dwell angle, turn the ignition OFF . Loosen the points hold-down screw, then adjust the point gap; increase the gap to decrease dwell, and vice-versa. Tighten the hold down screw and check the dwell angle with the engine cranking. If it seems to be correct, install the cap and rotor, then check dwell with the engine running. Readjust as necessary.
- Run the engine speed up to about 2,500 rpm, then let off on the accelerator pedal. The dwell reading should not change. If it does, a worn distributor shaft, bushing, cam, or breaker plate is indicted. The parts must be inspected and replaced as necessary.
- After adjusting the dwell angle, go on to adjust the ignition timing.