removing the air filter will allow more oxygen to get in, which will reduce the CO2, and a new set of plugs will allow the fuel to burn better - again improving CO

There was some stuff I put in a tank of fuel I got from a friend in the trade - my god it lowered my emissions no end! they were 7% (3.5% limit) on test one - took the long route to the test station after filling the tank with fuel and adding this additive - emmissions dropped to 2.9%