Just had my 94 Accord LX inspected and it failed due to high CO emissions during the high speed part of the test. Everything else passed the emissions test perfectly except for this. The guy who did the inspection said that he had never seen this before. Anyone have an idea of what could be causing this problem?

 

Spark timing back too far? Advanced timing gives more NOx but retarded timing gives more unburned HC (which includes CO). But it seems strange to get CO without elevated HC?

I don't know enough about catalyst activity to say whether it's related to a bad cat, but ???