weird smelling smoke!?! please help!

thanks for the input. mopar to ya, when I was running my cast heads it would ping but now that im running the aluminum heads it no longer pings. I just run pump gas. and so does anyone know if the colder plugs are ok to run or should i use hotter plugs? Sirdan, would it be leaning out even though it still smelled very rich? because when i went to the smaller jets it was as if I didnt change anything because it was still rich, and performance was about the same, it just did the backfiring thing. Thanks again. -Kory