During complete combustion, the typical combustion products from engines are carbon dioxide, nitrous oxides, particulates, water vapor, and numerous other contaminants. Several of these combustion products are linked to health problems. During incomplete combustion, carbon monoxide, a deadly toxin, is produced. The effects of carbon monoxide at low concentrations mimic common influenza and often are not recognized. High concentrations of CO interfere with thought processes complicating the diagnosis.
Carbon monoxide is a cumulative poison which can rise to harmful levels in the body in minutes.
In 1968 the EPA regulated CO emissions from on-road motor vehicles. Engines used indoors were not originally regulated. Recent regulations affect small engines such as those used on lawn mowers, chain saws, weed eaters, electric generators, water pumps, and boats, although the regulations for small engines will continue to allow considerably higher CO concentrations than the tighter regulations for on-road motor vehicles. Carbon monoxide is produced during incomplete combustion. Anything that leads to incomplete combustion increases CO production.