i remember when i had a gn400, it was bloody awful in absolutely every respect but one. the engine was fabulous, but it had a crap frame awful running gear, terrible styling, and inexplicably, 6v electrics. after a year of ownership i threw it all away, all except the engine. that i shoehorned into a twin shock honda xl185 frame. it still had crap electrics, but suddenly it was a hoot to ride and i could bimble offroad too. anyhow, one of the mods i did to the engine was to fit the carb off a kawasaki klr650, it was a cv flatslide and was fecking huge, iirc it was getting on for 40mm and the bike went like merry hell with it on. i could cruise at 80mph and it would just touch 100mph on the motorway. amazing for a lowly gn motor, most of the added oomph i put down to that whopper of a carb.