How about a crf150r motor swap?

I saw a nice vintage st90 with a rebel 250 motor swapped in at a bike show last month.
very sanitary job and purred like a kitten.
yeah-I think the 750 would be sick but the 150r would be a little monster without any weight gain.
upright cylinder, carbureted, and water cooled are the 3 main challenges I see.
i just don't think you could mod the stock engine to compare even at 200cc.

Yes I stand corrected-5 speed-maybe that is what I will do with mine as there is nowhere in nj to ride legally offroad unless you or a friend own acreage. Anyway the blank inside covers look like a perfect place to mount radiators-Honda should bring out the 2015 Grom 150r for $3999 with this setup as a pocket racer-would create a new class.