Not the supercharger, check your Boost control valve. Here's a few pics and what you should try doing:
http://www.mccgp.com/upgrades/boostb...ost_bypass.php
Also before bothering with this look at the shaft comming from the bottom of the valve, it should rest flat on the screw on the supercharger. If not, try this adjustment and if it still doesn't work you need a new Boost Control Valve.