I checked the site again to make sure I didn't post something we couldn't reference: http://www.ehobbytools.com/en-us/dept_8.html
This site uses the drill# which also has a decimal equivalent. Most of the kits on that site have the drill sizes we need so it is a good reference. A good kit for us would be one that has Drill#65 to Drill#78 or so. The decimal equivalent of a Drill#65 is 0.0350 and the Drill#78 is 0.0160. Most of the carb jets I have redone on these Chinese 80cc carbs start out around 0.030 and you go up or down from there as you know. I would guess that if you were to drill your jet ( I know you already filed it ) it would be good to step it up 1000ths of an inch at a time. Using Drill#68(0.310) do a test ride and see if the engine runs smooth thru the whole RPM range, if it hesitates on the low end go up one thousands to Drill#67(0.320) and keep going up one at a time until the engine runs smooth thru the whoe rpm range. Then when it feels good riding it - the spark plug will tell you when it is perfect by looking for a light brown to grey color on the electrode. Black and sooty sometimes wet=too rich. Hope this helps
Hey quarkdude, I finally got my drill bit set the other day. this evening I decided to pull apart the new carberator I havent messed with and check the initial jet size. I came up with a #71 .027 I went ahead and drilled it up one size to a #70 which I believe is the size you ended up using at .028. Ill start with that and see what happens. I must say people dont follow my example with the file idea its a no no.