Unplug all major electrical components     (one at a time) and lay a
coating of die-electric grease on all the plugs, of said components. (
including plug wires at the cap and plugs )
Spray some LPS, or WD-40 inside the cap and distributor, and on the
outside of the coil.
Now see what happens.
Mine always acted up when there was any moisture in the air, or on the
ground, and this procedure eliminated the problem.

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Terry 85 GL