Another problem that can occur is when the distributer shaft bushings get worn. When this happens the ignition points drive the shaft off center which causes the trigger points to open different amounts. It could cause more than one set to be open at the same time and could also make it so that certain trigger points never open, especially at slow speed.

Try removing the ignition points and see how the trigger point activity changes in your cranking tests. In cases where this happened switching to an optical trigger for the ignition can extend the life of the distributer.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician