See Figures 1 and 2
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 degrees dwell and the maximum figure for that setting. Never attempt to adjust the points when the ignition is on, or you may receive a shock.
On trucks with electronic ignition, the dwell is pre-set at the factory and is not adjustable.
ADJUSTMENT WITH A DWELL METER
When working on a 1975-77 truck, be sure to see the precautions noted in the following Transistorized Ignition section.
Connect a dwell meter to the ignition system, according to the manufacturer's instructions.
- When checking the dwell on a conventional ignition system, connect one meter lead (usually black) to a metallic part of the truck to ground the meter; the other lead (usually red) is connected to the coil primary post (the one with the small lead which runs to the distributor body).
- When checking dwell on a model with transistorized ignition, ground one meter lead (usually black) to a metallic part of the truck; hook up the other lead (usually red) to the negative (-) coil terminal. Under no circumstances should the meter be connected to the distributor or the positive (+) side of the coil. (See the "Service Precautions'').
- If the dwell meter has a set line, adjust the needle until it rests on the line.
- Start the engine. It should be warmed up and running at the specified idle speed.
- Check the reading on the dwell meter. If your meter doesn't have a 4-cylinder scale, multiply the 8-cylinder reading by two.
- If the meter reading is within the range specified in the "Tune-Up Specifications'' chart, shut the engine off and disconnect the dwell meter.
- If the dwell is not within specifications, shut the engine off and adjust the point gap as previously outlined. Increasing the point gap decreases the dwell angle and vice versa.
- Adjust the points until dwell is within specifications, then disconnect the dwell meter. Adjust the timing as detailed in the following section.