follow the cable down to the carb rack. there will be a rubber boot over the adjuster nut. pull the boot back, pull the cable straight up and measure the distance between the cable and the top of the nut. your looking for 21-23mm of cable.
tightening the adjuster nut increases the cable length(turning it in towards the carb rack). turning out decreases the cable length. dont forget to set the jamb nut when your done.