How to get black exhuast without diesel (maybe and additive???)?

okay i want to make my lawnmower (its more or a offroad racing mower now) hav black smoke because it just looks so cool and i didnt want to switch to a diesel setup or run diesel gas for that matter, isnt there something cheap i can do or just add to the gas to make it smoke black, and i know about the whole running it rich or lean to make it smoke, mine is running just fine, but i want it to exhaust with black, a 30hp engine with 2 chrome stacks and 32' boggers in the back and 20' boggers in the front without black smoke, sigh... its just not cool lol. Would adding like food dye or tattoo or regular pen ink to the gas make it smoke black or just burn up and do nothing someone help me please!!!