On most 4st. motocross bikes under the air filter is a restrictive backfire screen. By using an air filter system without the backfire screen. When you increase air flow which will increase power. Usually, you can expect 1-2 hp gain with better throttle response.
There is also a second problem the OEM filter is only held down by two clips. The clips do not hold the air filter down very tightly, dirt may get past.
For a note - I have used the No Toil Super flow kit on a few Yamaha over the past few years and always worked great.
The Twin Air kit uses an aluminum cage to replace the backfire screen with a flame-resistant air filter and lock down screw for the filter.
Thick, flat foam, greaseless sealing ring ensures maximum contact with your air box while acting as a breathable gasket for increased air passage. Smaller than stock to increase air space and circulation around filter
The No-Toil Super-Flo Kit uses a plastic back-fire screen-less cage, a pre-oiled flame-resistant filter, and a new filter lock down screw.
The best part about installing either the Twin Air or No Toil Kits, you will feel the difference in POWER.