Grip Removal and Installation 
 
-  Very small, thin straight-blade screwdriver
  Supplies 
 
-  Lacquer Thinner
-  WD-40
-  Old towel
  Removal 
Slide the screwdriver between the grip and handlebar or throttle drum.
Squirt WD-40 into the opening.
Wiggle the screwdriver to spread the WD-40 around.
The grip should slide off.
  Installation 
Thoroughly clean the handlebar or throttle drum with lacquer thinner.
Thoroughly clean the grip with lacquer thinner.
Spread the towel out underneath the grip.
Pour lacquer thinner in the grip and shake vigorously to coat the inside.
Slide the grip onto the handlebar before the lacquer thinner inside the grip can dry (approximately one minute). 
Once the lacquer thinner has dried, the grip will not move.
Source:  
http://www.st-owners.com/forums/showpost.php?p=593440&postcount=67
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MarkFeit - 23 Nov 2008