Rough idle and takeoff 250 inline

[68gmcdude]

I have changed the points, condenser and spark plugs. Point were set to. 019 gap according to the manual. Timing was off and is good now. Seems to be idling better but have yet to drive it. Hooked up a dwell meter and it is only reading 24. Should be 31-34 according to the manual. I keep reading that the dwell/ points should be set with the motor cranking, not with a feeler gauge. I have never done this. How do you do this by yourself? And how do you keep the motor cranking while adjusting the dwell / points?.... Help? Thanks!