This is fuel starvation, start by replacing the filter in the tank, check fuel hose for trapped, kinked, or cracking.
Dirt may now be in the carb, remove the carb, remove the pump cover ( usually held with one philips head screw ) here you will find a fuel screen, either clean or replace, if you have done all these things and it is no better you can now open up the L screw on the carb half a turn ( counter clockwise, to richen up ) do not advise you touch the H screw unless you have a taco to check free running revs.
Husqvarna man, November 2009
