Note that the amount of smoke the engine produces is highly dependant on factors besides how rich the engine is. Things like the brand of fuel (or, more to the point, the brand and types of oil in the fuel) can affect how much smoke is produced, and other factors such as lighting, wind, and the prop used can affect how visible the smoke is on the ground.

I use the pinch test, and find it works very well. When I can't pinch the fuel line, such as on a cowled engine, I peak up the engine, then open the needle a little at a time until I hear the RPM change. On many engines, 2-3 clicks isn't enough, you want to hear the RPM come down off peak.