I'm assuming you have slack in the cable and want to remove it. If so:
Make sure one of the cables isn't in fact the electrical wiring from the handlebar-mounted switch. If you really do have two throttle cables, one pulls the throttle open, the other closes it. To find out which is which, grab one cable housing and gently pull it away from the handlebar. While doing this, look at the left side of the carb, where the cable connects. If the housing is easy to pull, and the carb. connection moves, you found the right cable. If not, try the other cable.

There should then be a rubber housing to pull back where the cable connects to the handlebar. This will expose an 8mm barrel nut about 1" long, and a 10mm lock nut. Get two wrenches of that size, or carefully use an adjustable wrench, and loosen them. Then rotate the barrel nut to tighten the cable and remove the slack.
After that is where you want it, screw the locknut back down onto and against the barrel nut.