You don't say what type of engine is ftted, but it sounds like it's running rich.
If it's a Briggs & Stratton with the carb on the tank, change the diaphragm.
If the engine (whatever manufacturer) has a choke butterfly, make sure it's not sticking closed.
Clean (or replace) the air filter.
phil_saunders@bigfoot.com
Phil Saunders, June 2008