I have had same problem. First time, I sent it out for fixing. They told me exhaust was clogged. They clean and it ran great. From then on, I started cleaning exhaust and intake myself. Also found manual online, which helped a lot. I've since then found out that the Mantis motors are similar (or a branch off) of Echo. So many parts are similar to their gas blower pack. Home Depot had a kit that had spark plug, air filter, and fuel filter in it all for ~$12. Had to tear off rubber from around air filter, but other than that had it running great in no time. I've also learned since finding the manual online, that the gear box should be checked/lubed each year, and also how to reseat motor on drive shaft, if slips off.

Good luck
Dan