First slug gets screwed in all the way towards the tip until it stops turning. Not too tight, but snug it up. Screw the next slug until its snug against the first slug and so on.
If running Ultimax belt, try the weights empty with NO slugs at all, then go from there.
If running 8jp belt put 3/4 inch slug (3.1 gram) in first, then screw 3/8 inch slug (1.3) behind it and go from there.
If it under turns, pull the 3/8 slug and replace with 1/4 slug.
Hope this helps.