BT-FN202 Air filters are use for NISSAN cars

BT-FT202: 201mm*215mm*30   package: 205mm*220mm*22mm   NISSAN

The air filter is located on the top of the carburettor or in the case of fuel injected cars to one side of the engine. Dirty air entering through the induction system can cause premature engine wear. The job of the air filter is to prevent this.
Undo the air filter-housing lid and remove the filter. Clean any loose material from the housing, but be careful not to let anything get into the carburettor as this can damage the engine.
The air filter is a paper element and it can be difficult to determine whether it is dirty or not. They are relatively inexpensive, so if in any doubt replace it. Dirty air filters cause high fuel consumption and the savings made on fuel will outweigh the cost of the filter.
Hint
If you are driving in severe dusty conditions you can fit an oil bath type or washable type air filter. They can be reused over and over and are available from good accessory shops.