Craftsman 580.752090 Operator's Manual page 35

Emission Information
Engines that are certified to meet the California Air Resources
Board (CARB) Tier 2 Emission Standards must display
information regarding the Emissions Durability Period and Air
Index. The engine manufacturer makes this information
available to the consumer on emission labels. The engine
emission label will indicate certification information.
The Emissions Durability Period describes the number of
hours of actual running time for which the engine is certified
to be emissions compliant, assuming proper maintenance in
accordance with the Operating & Maintenance Instructions.
The following categories are used:
Moderate: Engine is certified to be emission compliant for
125 hours of actual engine running time.
Intermediate: Engine is certified to be emission compliant
for 250 hours of actual engine running time.
Extended: Engine is certified to be emission 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.
Certain engines will be certified to meet the United States
Environmental Protection Agency (USEPA) Phase 2 emission
standards. For phase 2 certified engines, 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 emission
requirements.
For engines 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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