In my latest quest for a carburetor which works I have tried about six different carburetors from the simplest to air bleed to RC carburetors. I have tried throat diameters from 1/4" to 3/32". On my latest engine with 1 1/8 dia cylinder I finally have ended up with 7/64 dia and I have found that the jet MUST have the taper on the end to direct the flow over the opening jet. Position of the jet into the air stream is also critical. I am presently working on making a simple single straight through carburetor using a Duclos type jet and and fuel bar. The present engine is an Atkinson Differential which due to the design has a very short compression stroke and other design flaws so it is fussier than normal. I find a carburetor which seems to work and I start and run the engine six times and I go get a cup of coffee and the thing will just refuse to start. I walk away for 15 minutes and when I come back it starts and runs again. It seems like there should be some basis for various variables so that it is somewhat less of a guessing game and avoids making multiple variations in order to come up with a working carburetor. Obviously there is a lot to the science of carburetor design.