ChrisS

-adjust the valves
-check timing
-clean and gap the spark plugs
-inspect air filter (replace if dirty)

-make sure the cat is hot when the test is done (i.e., driven for 15 to 20 minutes at freeway speed then test immediately)

-think about replacing the catalytic converter (they do get tired after a while; around $110 shipped to your door)

What kind of smog test does MD do?

My car is a stock 1991 Si with the original D16A6 no mods, California emissions.
Here in California, the engine is tested under load at 15MPH and 25MPH.

Last smog test (after two years and 13k miles on the cat)
HC (PPM) 134 max at 15, 108 max at 25 (measured 52 and 42)
CO (%) 0.82 at 15, 0.71 at 25 (measured 0.16 and 0.21)
NOX (PPM) 847 at 15, 786 at 25 (measured 832 and 397)
My car is fine for HC and CO. But, NOX is getting near the max at 15MPH 832 (only 397 at 25MPH; probably because cat heated up)

My previous smog test with a brand new cat.
-everything measured extremely low
HC 6 and 3
CO 0.00 and 0.00
NOX 56 and 43

Take Care,
ChrisS