Cars, etc.

[Bob Zumbrunnen]

I don't think it's as common a problem as it used to be, mainly because cars running leaner nowadays and thanks to fuel injection and tight computer control, they stay right in the optimum fuel/air ratio range all the time rather than running "fat" in some areas like was unavoidable with carbs.

But I still see that familiar coloration in the tailpipe of modern cars. My guess is that carbon is an unavoidable by-product of internal combustion engines running on current fuels.