Briggs & Stratton Murray 2691762-00 Operator's Manual page 17

Engines at or less than 80 cc displacement are certified to
be emissions compliant for 50 hours of actual engine running
time. Engines greater than 80 cc displacement are certified
to be emissions compliant for 125 hours of actual engine
running time.
Intermediate:
Engines at or less than 80 cc displacement are certified to be
emissions compliant for 125 hours of actual engine running
time. Engines greater than 80 cc displacement are certified
to be emissions compliant for 250 hours of actual engine
running time.
Extended:
Engines at or less than 80 cc displacement are certified to be
emissions compliant for 300 hours of actual engine running
time. Engines greater than 80 cc displacement are certified
to be emissions compliant for 500 hours of actual engine
running time.
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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