There is a lot to setting up triple webers. In a nutshell:
1. Engine is in good order (valves, ignition, timing, plugs, wires, manifold sealing, etc).
2. Linkage is non-binding and has exactly the same start, stop, and throw distances on all 3 carbs.
3. The carbs are in good order.
4. The jets, chokes, fuel levels, series number, etc are the same on all carbs AND you are in the ball park for jet and choke sizes for your engine/application
5. You have the tools and knowledge to tune triple webers: http://240260280.com/Tech/Carbs/Weber/DCOE Theory Operation and Tuning.html
Get one of these for sure:
or