Briggs & Stratton Vanguard 290000 Operator's Manual page 15

For example, a typical walk-behind lawn mower is used 20 to 25 hours per year.
Therefore, the Emissions Durability Period of an engine with an intermediate rating
would equate to 10 to 12 years.
Briggs & Stratton engines are certified to meet the United States Environmental
Protection Agency (USEPA) Phase 2 or Phase 3 emissions standards. The Emissions
Compliance Period referred to on the Emissions Compliance label indicates the
number of operating hours for which the engine has been shown to meet Federal
emissions requirements.
For engines at or less than 80 cc displacement:
Category C = 50 hours, Category B = 125 hours, Category A = 300 hours
For engines greater than 80 cc displacement and less than 225 cc displacement:
Category C = 125 hours, Category B = 250 hours, Category A = 500 hours
For engines of 225 cc or more displacement:
Category C = 250 hours, Category B = 500 hours, Category A = 1000 hours
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