Here is an interesting article on the emissions problem of big 650 singles and their decline. I like what Chris Scott said.
“I am definitely over 650 singles as they are now,” Scott says. “On the dirt, the big single power pulses make nadgery sections awkward where the CB-X twin rolled through smoothly. A single of 450 or less or a twin up to 650 will do me nicely. I can see myself flitting between the two in the coming years.”
That is pretty much where I have landed with my 650 V-Strom and CRF 250L. However, if this article is correct, it will be sad to see the cool old thumpers go away.