NOx is generally the result of really high temperature exhaust. I would richen the mixture slightly to lower temperatures, or advance the timing slightly. I think that will cool the engine down enough.

Moreover, it is formed at higher combustion temperatures, oxygen and nitrogen fuse at temperatures of something like 1400-1600° F and during the rich burn cycle, NOx is reduced. The lean burn cycle converts the hydrocarbon and carbon monoxide emissions. That's why O[sub]2[/sub]S switch between rich and lean, for the catalyst to work properly. The EGR's sole purpose is to reduce this particular gas by actually lowering combustion temperatures, a rich condition is introduced when the EGR is open (exhaust gas is low in oxygen) and thereby creates a rich air / fuel ratio, which reduces cylinder temperatures. A hotter running engine is more efficient but will not reduce NOx emissions, the proper emissions equipment is required for that. A fat tune will reduce NOx but may put you at risk of exceeding HC emissions.

Praveen-Kumar

oxygen and nitrogen fuse at temperatures of something like 1400-1600° F

thanks for confirming the temperature range.....