Join Date: Jan 2004
Location: Green Bay, Wisconsin, United States.
It really depends what emissions we're talking about actually, i beleve its NOX (oxides of nit) that go up as running a lean mixture.. Other emissions may go up or down depending on what the mixture is.
But to answer the first question. Stochiometric mixture (14.7 parts air to 1 part fuel) As you know air is only has so much oxygen in it, which supports combustion, if you dont have enough air(oxy) to support the combustion the mixture is considered rich, too much fuel, not enough oxy to burn all the fuel.. Vice versa with the lean condition. Running lean also means running hotter, which has been said.. Just like a torch, you add oxygen and the flame can get 10x hotter then just a standard acetylene flame.
Jetting for carbs is what changes this mixture, different circuits for different throttle ranges.. Talk to people who ride snowmobiles in the mountains, we've gone to higher elevations and had to change jets just to get the sleds running decent, and not burning holes in the pistons..
At least with FI the ecm program can be changed quickly, changing pulse width and controlling fuel like that, all we need now is an 02 sensor to see what, if any oxy gen is coming out fo the exhaust..