Smog test NOx help

[cornutbuzz]

Hello there! My 1987 300ZX (Z31) just passed the California smog test in every category except the NOx reading. It passed the NOx test going 25mph, but not going 15mph. One of the technicians at the smog test center told me that auto part stores sell a kit that can fix this problem (and said it's only about 20 bucks), but he couldn't give me any additional details. Does anyone know what he's referring to?

[PapaSmurf2k3]

Maybe the "kit" he's referring to is snake oil.

You can probably get it to pass by adding some alcohol (like ethanol) to the gas, or retarding the timing if you have enough of a buffer between where you were running and the HC smog limit. Retarding the timing should reduce NOx, but raise HC.