There is a cable adjuster for the throttle cable, up by the front brake master cylinder (more adjustment is available at the carb, if needed). The return cable needs to be adjusted at the carb and the gas tank will need to be off. Just press on the cables, like the arrows, and tighten until there is just a tiny bit of slack. I tighten my throttle until I can't hear the 'closed click' in the carb
(not the throttle tube), then loosen a half turn or so.
There must be a tiny bit of slack in both cables when you're done.
Pic stolen from Wibby, post #1287 in the DR650 thread:
Originally Posted by Jon_PDX
And be sure to double check the slack at full right and left turn of the bars