Air shifters on bikes can either use a fuel cut or spark cut to bring down the RPM. Cutting the spark means there will be extra fuel coming into the cylinder and it will backfire as soon as it ignites again which can be cause damage to your exhaust manifold. But apparently it's a little bit faster than doing a fuel cut. Anyway my point is that it might be easier/better to just use a fuel cut. If you're doing a button shifter instead of automatic then you could just let off the gas and avoid the need for all that in the first place but once again it's gonna be slower. If you want to keep your foot down maybe you can just connect the Arduino to the wire coming from the fuel pump or something.