You must really hate dirt...
...
I think alcohol would cost a fortune...
Diesel would be even dirtier...
... I'd check into natural gas...
...or,.. just make sure your bike is tuned good...
The first year I owned my Savage, it had to be emission tested... and it's emission reading was so low, they had to sock the entire muffler to get any reading at all...
This was probably due to them messing around, making me idle for 10+ minutes until the engine was getting hot...
Tuned well, it can run very clean...
Don't try to make your idle real low, or make the bike run lean... that will increase emissions...
Keep the idle up at around 1100rpm,.. and tune the jetting for maximum performance...
Maximum performance = most efficient fuel burning, and least emissions....
In good tune,.. your bike should average about 60mpg...