What engine is fitted? If it's a Briggs carb-on-the-tank engine, I suggest replacing the carb diaphragm. If it's a Briggs with a primer on the FRONT, I suggest a ruptured air-cleaner gasket.
If it's NOT a briggs engine at all, come back here and I'll advise.
phil_saunders(a)bigfoot.com
Phil Saunders, May 2009