to be honest, the standard settings on your carb will be a pretty good compromise for low and mid range engine speeds but unless youve done a sustained high speed run then you wont know if its running ok. removing restrictions in an exhaust system will make the engine run lean, removing restrictions in the inlet side will make the engine run lean, doing both and then not correcting the jetting is asking for trouble. running lean will result in either a hot running engine, a burned out exhaust valve, or worse, a holed piston as the heat just builds and builds the longer you have the throttle on a high opening. this can occur after just 5 or 6 miles on the motorway. unless your checks have been with the engine under load on the road at high speed, id be very wary about closing the door on this just yet. set the carb up right and your gn will fly, better still, get a carb off a klr650 and fit that, i had one on my gn/xl hybrid and it would just about crack 100mph on the long downhill bits of the motorway, no mean feat for a 400cc off roader with a lazy custom bike engine in it!
