You should be able to see if the cable is being pulled or not, and if the pads are pushing against the rotor. Those pre '03 rear brakes are tricky though. When you put the pads in you have to do it just right or it won't work right. I have an '02 and don't use my rear brake 'cause it works so bad. Go hydraulic. Get post '03 Blaster, Banshee, or a Warrior rear brake like blaster99 said. That is what I plan to do. Same with the front brakes. Put some hydraulic discs on it. Those drum brakes are crap.
'02 Yamaha Blaster - '03 Front Hydraulic Disc Brakes, Elkas on the Front, +3+1 ASR a-arms, DG Bumper, PB Phantom Exhaust w/Spark Arrestor Kit from ALBA, Renthal Bars, Premix, No Air Box Lid, Uni Air Filter, UM Swinger Skidplate, AC Nerf Bars, Holeshots all around