This sound like a timing issue, Check the points for proper gap, ck for proper timing, also ck the distributor shaft for looseness, or wabble, remove the cap and button and grab the shaft with your fingers and see if it moves back and forth, not in/out thats ok, but in a side to side type of movement. This can cause a missfire at hi rpm.
Answers & Comments
This sound like a timing issue, Check the points for proper gap, ck for proper timing, also ck the distributor shaft for looseness, or wabble, remove the cap and button and grab the shaft with your fingers and see if it moves back and forth, not in/out thats ok, but in a side to side type of movement. This can cause a missfire at hi rpm.