It is possible to assemble the floats upside down. The lift pins on the floats are off set so if they are in upside down they in fact lock the float valve open hence the flooding. A simple test is to gently shake the carb when assembled, you can hear the float movement if they are free to move ie float.
With ref my earlier post about carb/starting problem, I stripped the carb completely, all jets out etc, clean with air line, reassemble with all vent pipes connected & wow what a difference. I tried the kick 3 times then leave for 5 mins method for starting which seems to be the answer, I guess the fuel vapor gets into the chamber as reqd. Choke off immediatly & blip till warm.
Guess the moral of the story is that a simple clean is often all thats required, I assumed the problem must be more serious, spark or ignition etc. So get you blow pipe out & start cleaning.