What would cause the HC levels on a smog check to be to high?

What is your question?

I got a 2000 Buick smogged today, the car passed, but the guy told me that I was putting out to many HC's. At 15mph I was at the max amount of 50ppm, and at 25mph I was at 31ppm (the max is 34ppm apparently). He said it passed now, but it would probably not pass next time unless the problem was addressed. Anyone know what would cause this? I had engine light go on a few months ago, but there hasn't been an issue with that during the warm months (not since early April). And it is about 1000 miles overdue for an oil change.