Normally the mag is connected to a cable. Sometimes you can make adjustments on the cable. In this case you want to try to make the cable longer. 
You will need to take of the cover.
If you could e-mail me a picture of the inside I may be able to tell you more.
Is this the bike you have ?
markepeterson@austin.rr.com
                
 Mark Peterson
                
 February 2008