OK, how's this?

Here's the EPA's exhaust emission standards for cars and pickups in grams per mile: http://www.epa.gov/OMS/cert/veh-cert/b00001a.pdf

Here's the EPA's latest figures for motorcycle and scooter emissions in grams per kilometer: http://www.epa.gov/OMS/cert/veh-cert/cert-tst/05m.zip

If you look at the THC or "total hydrocarbon" and CO or carbon monoxide standards in the first document, and you convert the test numbers in the second from gm/km to gm/mile, you'll see that only 8 models of motorcycle / scooter (or more precisely motorcycle / scooter engine) fulfill the least stringent 5-year standard for hydrocarbons and only 22 models for the equivalent carbon monoxide standard.

Incidentally, you'll note that the Westward Industries GO-4 Interceptor II does execeedingly well on both fronts, and would be a good choice, if you're looking for a motorized two-wheeler.