You sell the parts to solve the problem...and you don't know anything about engines? Remember, air and fuel. Whatever you use in China must be as clean and pure as is in America. If you use shetty gas, and cheap oil, your saw won't offer the power its designed for. Likewise, hipppaa, your air quality is 1/2 that of North America. Therefore, a 9th grade science major, here or there, would tell you, the power drops when the saw is run in smoke.................rising from the river.
Be more specific, and we American forum members will cheerfully collectively solve your problem. Start with a new saw.............they are cheap.