Honda CRF50F 2004 Owner's Manual page 151

Emission Control Systems
Problems that May Affect Motorcycle
Emissions
If you are aware of any of the following
symptoms, have the vehicle inspected and
repaired by your Honda Motorcycle Dealer:
1. Hard starting or stalling after starting
2. Rough idle
3. Misfiring or backfiring during acceleration
4. After-burning (backfiring)
5. Poor performance (driveability) and poor
fuel economy
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Technical Information