drill a 1/2" hole in the top flat of the cap about 2/3 of the way between the center terminal and the #1 terminal and freeze the rotor w you're light & check rotor phasing. Use a junk cap if need be. I'm assuming the plates and the pickup assy are not loose. What gap are you using? since this is a problem case, check all 8 vanes w the brass gauge & I like .006 on the tightest one keeping mind that the vac can changes phasing and gap and w a Mityvac I find the tightest place on the tightest vane and set that one @ .006. Also check the ohms of the pickup & lastly if still no go might cut the 2 pickup wires and switch polarity then retime it as you're gonna replace it anyhow. Holler back w any news.