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.

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There are two companies that make kits to eliminate the Backfire screens TWIN AIR COMPLETE POWERFLOW KIT or NO TOIL SUPER-FLO KIT.

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

Twin Air Powerflow Kit Air Filter Kit Yamaha YZ450F 14-17 / YZ250F 14-18 - 152219C

Twin Air Powerflow Kit Air Filter Kit 18-22 Yamaha YZ450F / 19-22 Yamaha YZ250F - 152222C

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.

No Toil Super-Flo Yamaha YZ250F 2014-2018 / YZ450F 2014-2017 - SFK18951

No Toil Super-Flo Air Filter Kit - YZ250F 19-21 / YZ450F 18-21 - SFK18053

The best part about installing either the Twin Air or No Toil Kits, you will feel the difference in POWER.