[Ross F-1]

If you use a MityVac hand pump it is easier to test for a leaky can. It should hold vacuum and you should see movement.

Always check the wire under the distributor plate for bare wire grounding out. I had a really vexing problem with one that stumbled horribly just off idle, and sometimes backfired. Turned out one of the screws holding the points to the plate stuck thru the plate more than usual, and would contact that wire each time the vacuum advanced or retarded.