I posted this a long time ago, but was too lazy to find it.
While you are "port matching" and doing all these other things to try to make your chinese two stroke a "fire breather" (lol!) You will want to check the tip or outlet of the exhaust.
I have found a few that were welded nearly closed when they welded on the "stinger" or outlet pipe. All the port matching and nitrous/"high performance" carbs (again lol) ect. aren't going to do anything if the outlet is welded in there and the weld has closed all but a hole the size of a pencil.
Check it first.