yeah, use the 5/8er and use plenty of cutting oil(any oil will work, or even wd40) to keep your carb and the bit cool. Otherwise you will bind up, fuck shit up, and maybe warp your carb if it gets too hot.
When you are finished, make sure you sand away any high spots or burrs by the slide.
And take out the emulsion tube as well as the jet. You drill into the tube, you are, Le Fucked.