[Funny]

If you plan to continue leaning out the mixture, you'll want to get an A/F meter to check to see how close to stoich you are. It is likely that if you don't, you'll cook your valves and cause brown deposits on your spark plugs. More instrumentation is required when modding a car than just a butt-o-meter. The other posters are correct, if you go too far away from stoichiometric mix, you create exponentially more NOx.