Other than sprocket (48 from JT Sprockets from a place in England), I never did anything to mine. The stock carb worked well, and I never played with the pipe. In spite of unknown damage following a serious accident when an SUV ran me off the road when I had about 2500 miles, I still managed about 10k miles on it commuting 33 miles a day year-round following the accident. Lack of skills and lack of interest have kept the bike sitting, and I commute on a TGB 150cc scooter.
With all the issues everyone has been talking about the Hawk from stock lack of power, gearing, carb, exhaust, my TMEC 200 didn't have any of that! Come to think of it, I don't think I ever touched the valves!! LOL And the engine is 'only' a 200cc, compared with the 22X of most of the new enduros. Officially, according to the EPA, the engine is manufactured by TMEC, but I was told by my friend who used to import/distribute them the engine is OEM'd by Zongshen, so that answers the reliability aspect of it. I could hit around 65 mph, but cruise at 60 stock.
Sunright is the only distributors of these in the US now.
http://www.sunright.net/linhai-scooters/denali-200xt
Which wheels/tires do you have? 17/17 or 21/18? Sunright only offers the 21/18. Mine is the 17/17