Did he wash the bike recently ?
I was yesterday going around with some of my TW friends
Basically all the TWs when max throttle at high speed they produce a lil bit of clear smoke, a very small small small puff, I guess is kinda normal
But one of the bikes produced a grey puff of smoke, sometime even one after another, like 2-3 puffs of smoke in 4-5 seconds
The smoke puff is kinda "big" like the size of a tire diameter, greysh coloured, and only when you use throttle a lot or when at high speed you open it completely
What can cause this?
Maybe idle mix screw?
The rings may be starting to get a bit worn. Black smoke is usually the carb misadjusted. I usually will just keep a good eye on the oil level and (if it's not real cold) add Lucas heavy duty oil stabilizer or use 20/50 weight on the next oil change. The Lucas may tighten clutches up which can adjust out. If you ride cold freezing weather I wouldn't do anything other than watch that oil level.
I think the TW was sending some smoke signals saying "HELP ME".
2013 Yamaha TW200
1996 Yamaha TW200
1995 Kawasaki KLR650
2002 Yamaha RoadStar 1600 with sidecar
Likely over-filled with oil - but you may want to check his air filter first, in case it's got either wet, or excess oil / fuel in there
Always look for the simplest fix first ......
Pretty much, yeah - easy to do if both wheels are not level
On the air filter, take a look at the tube underneath the air filter box - if there's anything in that tube, that may be the problem
Sounds like oil smoke, maybe rings, maybe valve stem seals, maybe both. If it only happens after extended high speed / wide open throttle runs I wouldn't worry about it. When / if it reaches a point where it is smoking all the time, or nearly all the time then fix it.
You can play with the carburetor if you want to but I really doubt it will make a difference. If the bike is running well I would leave the carburetor alone as chances are it will run worse after "adjusting the carb." and it will still smoke.
Long live the internal combustion engine!