Originally Posted by
skywagon
Mag problems at low RPM's is usually caused by the point gap closing to a bare minimum. This is caused by the fiber points bar on the points that follow the distributor cam action. If the cam gets dry, dirty, etc. it will wear down the rubbing bar. The results are the slow closure of the points gap. At high RM's this closure is less noticible due to other forces working on the points and electrical spark generating system. However, that RPM range will soon have problems also.
Rule of thumb....check the mag points and gap at every 50 -100 hrs. After the points are checked or re-set, the timing should be checked too......