Drilling the jet

You should do a plug chop to check.
Here's a link: http://motorbicycling.com/showthread.php?t=42595&page=2
Best quick way to see if you are in the ballpark is to turn off the fuel petcock and keep riding until it runs out. If it runs better right before it stops, you might need a smaller jet.
If it seems to fall flat past 3/4 throttle and seems weak, chances are you're too lean already.
ALWAYS pull a plug chop after changing jetting.
Best thing to do is jet it for max power and running manners, then back off a size for reliability.
Running too lean can destroy a motor in a very short time so BE CAREFUL!

You just reuse the same plug. Until they are worn, spark plugs often clean themselves at operating temperature.

If it's really sooty, a little TLC with a brass-tooth brush should take care of it.

if you get WOT to run right, then you often have to do a lot of trying diff settings on needle & float level until you get acceptable power thru the full range (sometimes requiring a redo of the main again)