Sorry Jack. Your last paragraph there is not true. The average motorcycle IS "dirtier"[emissions-wise] than your average modern passenger car is today. Many, if not the majority of privately owned motorcycles in this country have had their exhaust systems and/or their fuel delivery systems modified by their owners after their initial purchase which contributes to this fact.
This idea that because motorcycles on average have fewer combustion chambers than does your average car, seems to contribute in keeping your "theory" alive with many motorcyclists, but once again, it's not true.
