best learn how to tune your engine then Pipe, then Clutch set up, then gearing and Car set up before Mod engine! If you can do all those right, you can reach A main in Hong Kong easily.
I spent too much time in Mod engine in pass, this is 2004 so I never run well!
this is standard on most .12 engine now. But another purpose to do this on a 2 stroke was to take out more or less material to Dynamic balance the crankshaft at a optimal rpm. For most Top end .12, we want to do so at between 38000 to 42000rpm.