You will need: Sisors, a hole puncher, a yoyo, a piece of plastic( I use the casing of electric tape) you could use credit cards, sand paper (optional)
Before
http://i48.tinypic.com/1zqdkwx.jpg
After
How to do them:
Step 1
Cut a small piece of plastic
Step 2
Make a hole with the hole puncher on the piece of plastic
Step 3
Some hole punchers make the hole too small, to make the hole bigger simply cut little by little the hole with the hole puncher until it fits the bearing sit
Step 4
http://i50.tinypic.com/ojqa0n.jpg I colored the shim so you could see it
When the hole fits the beaing sit cut the sides sorrounding the hole until it a little bigger than the bearing sit
Tips:
-At first the shims wont be how you want them but with practice they will
-If the shims are slowing down the yoyo it because they are touching the shields, simply deshield the bearing
-If shims are too big simply sand them
-If you want your shim to be rounder sand it till its round
Enjoy your home made shims
About Step 3
If your hole puncher make the holes too small to fit on the bearing sit you do the cuts on the picture above, an alternative is to sand the hole until it fits the sit.