The high and low screws have caps because the carb settings are set in the factory for the best emmisions, the caps are put on in such a way that you can only lean the mixture off, increasing the mixture will produce more emmisions, if the machine is running rich this is more likly that the needle in the carb is leaking, and thus the engine is flooding, a pressure test of the carb will quickly tell you if this is the case. The caps can be pulled back, there are special tools to do this, but leaning the mixture to compensate for a flooding carb is not the way forward, so a carb test and service is the best way to go.
Husqvarna man, March 2010
