My 48 HRD Rapide, built up from parts, has 67 miles on the rebuild and idles and runs a bit lumpy, but accelerates well. On the advice of another, I purchased a Gunson color tune to check the mixture at idle. My current set up is 32 mm Amal Mark 2 carbs, K and N conical filters, 106 needle jet, main jet 240, pilot 25, needle in third position and 3 1/2 slide. My pipes are a little blue. I warmed the bike up with a 12 mile ride and then inserted the colortune on the front cylinder running a fan on the engine. My mixture screw was about one and 1/2 turns out. The color flame was orange/yellow at idle, not unexpected because of the somewhat sooty plugs and lumpy running, but to my amazement, no amount of turning, in or out produced the desired blue color, supposedly representative of ideal air/fuel ratio using this tool. Any thoughts or comments will be appreciated. Thanks, Charles Cannon