The PAIR Block-Off Plate is a solution for sealing off the air injection system present in the following bikes: CRF300L/Rally, CRF250L/Rally, Rebel/CMX 300, CBR250R, CBR300R, and CB300R/F. This system injects fresh air into the exhaust port to burn off residual hydrocarbons in the catalyst. However, when an aftermarket exhaust system is added, the bike can develop deceleration popping due to the PAIR system injecting air into a fuel-rich environment. The PAIR Block-Off Plate can significantly reduce this popping. Removing the PAIR system can also help reduce the bike's weight by eliminating actuators and air hoses. Moreover, if you plan to run a wideband oxygen sensor in your exhaust, removing the PAIR system is essential. This is because when the PAIR system is active and closed loop fueling is not active, the air-to-fuel ratio will read lean, causing inaccuracies in the readings. Removing the PAIR system allows for accurate air-to-fuel ratio measurements using a wideband oxygen sensor. To install the block-off plate, follow these steps: Remove the barbed PAIR fitting attached to the top of the valve cover. Take off the reed valve assembly. Disassemble the reed valve from the gasket assembly using a Phillips screwdriver. Remove the backfire screen from the PAIR assembly. Install the gasket assembly back in the valve cover. Attach the block-off plate. Place the barb plug on the airbox port.
