I was leafing through this old Petersen motorcycle mechanics book, when I came upon a picture of Jerry Branch using a Tillotson diaphragm carburetor on a Rapido hop up. This brought back some ancient not so pleasant memories of a rescued Sears moped amateurishly outfitted with a chainsaw carb. At the time, at 14 or 15, we knew even less about a diaphragm carb then we did about the Mikuni carbs on the little Japanese bikes we were playing with. The moped ran only once in our care, wide open till it stopped by itself. My next experience with diaphragm carbs were the $50 non-runner snowmobiles that we could never make run long enough to foster anything but utter hatred for the things.
In retrospect if we had just installed a new set of points/condenser and a new diaphragm, I'd probably still be riding the them. But at the time... puller? ignition? carburetion? all black magic...
So I googled a bit and found that that type of carb was used in karting and even original equipment on Harleys. Lots of info out there... and the most amazing thing is now you can buy replacement Chinese diaphragm carbs for chainsaws, $20, just bolt on- they don't even need adjusting.