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Nissan Maxima produced high HC during smog test at 25 mph

I have a 1989 Nissan Maxima. I just passed my biannual smog check at a test only shop. When I look at the ASM Emission Test Results, I noticed that the HC (PPM) @ 15 MPH, my measured is 69 which is well below the Max of 80. However, @ 25 MPH, my measured is 60 which is very close to the max of 62. What can I do to reduce the HC at 25 mph? Thanks.
Answer:

You really want HC emissions between 0 and 20 parts per million (ppm). Although HC emissions passed at 15 mph, 69 is still very high and indicates your Maxima has an overall high HC problem. HC is raw fuel. High HC means your car's engine is not burning fuel efficiently. This may be due to a few different things. It is possible the ignition system isn't providing proper and timely spark, it is possible too much fuel is being delivered to the engine (rich fuel misfire), and it's possible not enough fuel is getting to the engine (lean fuel misfire). We'd recommend beginning with an ignition system test, and then a fuel feedback test. Much of where the diagnosis should start depends on the CO emissions your Nissan produced. Low CO would indicate lean air/fuel ratio. High CO would indicate a rich air/fuel ratio. In both cases this is an indication of a fuel management problem. posted by SmogTips Support

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