Reply To: Exhaust Pipe Size gt650 carby
Depending where the pipe is cut, the exhaust may even downsize to less than 51mm if its cut down too far.
So at the 3 bold flange , go inside the exhaust hole, get a vernier caliper and measure the hole size , if its something like 47mm,. then the exterior would be about 49mm (depends how thick the wall is. Measuring the diameter outside is better if you can.
You are right to ask, some 650 owners chop their pipes and put some kind of adapters (makeshift) or even make entirely custom pipe setup if the old system is corroded,
Measuring is the best way to be accurate (and i will assume you still use OEM pipes)
Take your time, no rush as we don’t ride much in this ice this week ourselves in the UK