OK when the screen is clogged barely any exhaust can mprobably get past it, remove the cover, get some gas and a toothbrush and try to clean it off, had the same thing with my blower.... clogged, it took around 75 pulls to start and it would die within a few secounds, cant accelerate either, and the muffler sounded weird.. soooo we took it apart found the muffler problem cleeaned it and took it out, first pull
hope that helps