Not the first time I've thought of this...but the exhaust of my 10yr old Kymco LIKE200I stinks!
The fumes are so bad that I always close the garage door before starting the LIKE out in the driveway.
Two points:
1) scoot runs great
2) mpg hasn't changed in years
3) it's been smelly for years
Simply do not recall if this odor changed after I tried fixing an engine stumble one year into ownership by swapping in a Yamaha motorcycle fuel pump.
If the oxygen sensor/cat converter has failed....it failed years ago!
Stig