I found a pair of Keihin PW20 carbs in my box of carb parts. I'm hoping to make one good carb out of two, for the project bike. I got them disassembled and in the carb dip for an overnight soaking.
I'm also modifying the original intake to accept this bigger carb. Instead of a 15mm stock carb, with it's tiny intake opening, I'm going to modify an old CB160 intake manifold so it can get welded up to the hogged out stock manifold. Along with the exhaust, some porting, and higher compression, this Yamaha GT80 engine should provide ample motivation.