Re: Dwell

[jlandry@domain.elided (John A. Landry)]

When he stopped taking his medication, strange voices in Terry Rust
<trust@domain.elided>'s head said:

>While changing points the other week I started wondering about dwell
>effects and realized that I can't remeber just what affect dwell has on
>things like performance and mileage. Can we tinker with point gap like we
>do with timing ? thoughts?

Terry,

"Dwell" is the amount of time - expressed in degrees of crankshaft rotation
- that the points remain closed.  When the points are closed, the primary
magnetic field inside the coil is being built up or "saturated."  When the
points open, the primary field collapses causing a corresponding high
voltage surge in the coil's secondary field and the secondary ignition
circuit (the coil, plug wires, spark plugs, etc.).

If the dwell is too small or "short" (points not remaining closed long
enough), well obviously the coil's primary field may not have time to
adequately build to its full potential.  The result is a weak spark in the
secondary wiring.

Having a dwell to large can mean the points don't open far enough to
completely break the primary circuit and the coil cannot fire the secondary
circuit.  Arcing and burning of the points can also be a problem with too
large a dwell.

The recommended dwell is therefore a range which tends to cancel out the
negatives.  It allows adequate saturation of the coil while at the same
time protecting the points and insuring reliable operation.

If you want to "tweak" the dwell, then try to set it on the high side
within the allowable range.  But you won't likely see or feel any
improvement as long as it's anywhere within the proper range.

With an electronic ignition system which doesn't use contact points, the
dwell is controlled by the electronic circuitry and cannot normally be
adjusted.

Regards,

John L.
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