Probably one of the easiest DIY maintenance you can do on your Himalayan.
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An air filter used in daily commutation bikes last for 15,000 to 20,000 kilometers, depending on quality of the bike as well as its running conditions. The purpose of the air filter is to shield the engine from dust and debris in air and improve airflow.
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You can also blow the air filter with pressures air and clean it that way and run for a few more Kms, but mine was done for.