Time to tune

A bushing determines the amount of mechanical advance in your distributor. It should have a blue 21* on it now. That may be OK depending on how much total you run. If you run anywhere from ~33-38 it may be OK. If the starter will handle more initial, you could put the black 18* bushing on it.

Springs that tend to work well are a light silver and med blue

I only back off timing to get a 1" drop in vacuum. Make sure you keep idle speed same when doing this. You may have a situation where the vacuum gauge method gives too much initial for the starter to handle. Use either the vacuum method or wherever the starer kickback.