Just because an engine is tuned to pass EPA specs, doesn't mean that its getting the best milage, especially when its leaned out to the point of running rough, and actually running better w/ the choke on 1 click. Most any engine is running the most effeciently, when it is running smoothly,....lets call it "correctly" But that doesn't mean that it isn't putting out more hydrocarbons. Remember in the 70s when carbs were leaned, ignitions and camshafts were retarded to pass the first emissions specs,....while at the same time miliage went down to an all time low ? But I was an auto tech in Ca then, so probably know more about that than some.
Ed L. wrote on 02/26/10 at 16:44:53: a stock engine is soo leaned out for EPA requirements you will get better gas mileage at a.....