240sx won't pass smog!

[1hot240sx]

Hello everyone, I just purchased my 1991 Nissan 240sx Fastback yesterday and I am very excited!

However, I did not pass smog and need to register the vehicle. The test ran back stating:

Hydrocarbons (HC) in Grams/Mile: my car, 2.10 applicable standards, 1.00 FAIL
Oxides of Nitrogen (NOX) in G/M: my car, 5.51 applicable standards, 2.50 FAIL

I passed my carbon monoxide with 11.29 when applicable standards is 12.00....


So before I go back for the third time and spend another registration fee, I changed the spark plugs, replaced the the fuel filter, and did an oil change all today. The previous owner did not care for the car too much for the car, but it still runs strong. What else do you think I need to do to pass emissions? Any advice would be greatly appreciated. Thank you.

[asoomal]

What are the O2 readings?

High HC and high NOx can be caused by a lean misfire, is it running rather rough?

[1hot240sx]

No, it's actually running pretty good, nothing rough, that's why I'm stumped. And where would I find the O2 readings? On the inspection report?

[asoomal]

I don't see why it wouldn't be on it, we have them lol.

Edit: Also check timing and set it back to 20BTDC.