Stihl MS180c no high rpm's

[fastback4]

I used it in May and now it has no high rpm's but idles fine. This model only has idle adjust, no high/low adjust. The chain lock is not engaged. If I throttle it up slowly it tries to get high rpm's but flutters out back to idle. I put on new filter and fuel lines I had for it and checked the needle and seat assembly and screen in the carb and brake cleaned everything well. New fuel, new plug, same results...no high rpm's...advise here please....Tom

 

[Fish]

Take the screen out of the muffler and clean, and also clean your air filter.