I worked on Stihl trimmer today that had a partially plugged muffler. Very hard to start and if it did start, it would not rev up and just died when the throttle trigger was pulled. Acted just like a lean condition or a carburetor diaphragm that was not flexing enough to open the metering needle. You can go to youtube to learn a whole lot about small engine maintenance & repair to help save yourself time, money and headaches or you can pay guys like me. I'm not being sarcastic, just truthful and trying to help.
Keep in mind that the ethanol in the fuel is causing a lot of problems in OPE and using a good fuel stabilizer such as Marine Formula Sta-Bil will go a long way to help prevent a lot of ethanol fuel related problems.