Air Filter

Please note that replacement of the stock air filter will, in most cases require rejetting. See Rejetting for more info.

Currently mentioned:

  • Stock
  • HiFlo
  • Uni FIlter
  • GSX 1400
  • K&N Drop in
  • K&N LunchBox /pods

For better engine breathing, the order of filters, from least to greatest, is:


The stock filter can be cleaned by dipping it in gasoline. It does have a finite lifetime, however, and must be replaced when cleaning doesn't work. It can be purchased through a dealership or online at any OEM supplier. Rejet is still recommended for a stock filter, due to the lean jetting from the factory for US models.

HiFlo Filtro

A replacement for the stock filter, it is available very cheaply. It does not require a rejet, though the stock rejet is still recommended.

Uni Filter

This filter, NU-2453, is made of foam and has mixed reception among the GSTwin community. If not properly cared for, it can dry up and tear during use, resulting in unfiltered air entering the carbs and possible jamming of mechanical components. However, other users have reported no problems even after several years of use.

GSX 1400 filter

twinrat reports that a GSX 1400 filter is a drop-in replacement, and does allow for more air through. (stock on left, gsx1400 on right)

Relative performance compared to other options here is unknown, so I just dropped it in here at a guess.

 - Phil B

K&N Drop-In

This filter, K&N SU-5589, replaces the stock air filter and drops into the stock air box. It can be used with a restrictor, to avoid the need for a rejet, or without.

Lots of nice comparison pictures, including the "restrictor" ring that you cant see while it is installed, at

K&N Lunchbox

This filter, K&N RU-2970, replaces both the drop in filter and the stock airbox. A breather filter, as shown in the picture, is recommended (but not really required due to factory steel mesh 'sponge' already under the breather cover) for the valve cover. This breather filter can either be a PVC filter valve (available at your local hardware store) or a breather valve like the one shown in the picture (available at your local auto parts store). The cheapest solution is a piece of shop towel covering the breather outlet to reject larger elements (sand, dust, etc). Keep in mind that the breather outlet is outbound, i.e. the combustion gases that get past the rings try to escape the engine case. BTW, that is the reason the breather hose in stock configuration is connected to the airbox -- to suck those gases out and back into the carbs to burn.

Rejetting is a must using RU-2970.

Specs: 2 3/8" flange diameter, 3 5/8" x 7 3/8" base , 3" long, 5/8" flange length, 4 3/16" flange center to center

K&N Pods

Pod filters, K&N RU-0800, are similar to the lunchbox. Most regard the lunchbox and pods as giving equal performance boosts. Once again, rejetting is absolutely required.

In the picture above, note the precharger bag over the left pod. This is available from K&N to extend the life of the filter in dusty conditions.

Specs: 2 7/16" flange diameter, 3 1/2" outer diameter, 4" tall

Universal clamp on Pods

These pod filters are knock-offs of the K&N ones. Some GSTwins users have bought them and reported no trouble, while others are wary of the construction and quality. If you do get these, make sure you keep them oiled regularly and inspect them for debris.

Specs: 60mm inside diameter, 3" outer diameter, 3" tall.

Breather Cover Filter

GSTwins member Wrecent_Wryder used the Uni UP-123 for his breather cover filter.
GSTwins member Paulin8r used the K&N 62-1320 for the same purpose


-Thanks to GSTwins member TheGoodGuy, who wrote the original FAQ