It's the over fueling. The "tune" makes it rich... like 90% of the Hardley's on the road, and, the cat removed, makes it mimic a Briggs & Stratton with the choke left on after starting, makes your eyes water. Just a guess... how close did I come?
There ain't nothing better than bike fumes ..... ahhhhhhhhh loooooovely when I was little and mum used to start her bike up I used to run out in the garden and just enjoy that heavenly smell ....
But being gased is another story
Hope you sort it