Just tried my new Colortune -- all in all I was quite satisfied with it and feel it did let me get even closer to an ideal mixture than the lift-the-piston method.

It could hardly be easier to use, the first photo show the basic set-up. The second photo shows the blue flame of ignition as seen looking down the tube.

It was at this point that I discovered that digital cameras really don't like to take pictures when you're holding them right next to a firing high tension lead... Yikes! Sort of scrambles their brains a bit. Fortunately no lasting damage was done and with a couple of tries from a more serene distance I was able to capture the result.