I would have not enlarged a stock dellorto! I run 16mm, 18mm, 19mm and 22mm dellortos on many of my bikes (all Tecumseh HS50 engines.) To be frank, i can not tell any performance difference. like none. as long as you have the jetting right, a 16mm and really no different than a 19mm. They look different, that's it. The 16mm and 18mm is upright, the 19mm is sideways. and the 22mm is just big. You get the performance gain when you switch from the crappy tecumseh carb to a slide carb. The size (16mm to 22mm), matters a whole lot less.