I use six Colortunes in my test engine for setting up carbs after I remanufacture them. When I am finished with my remanufacturing efforts the carbs have: ideal shaft/bearing fit; the throttle bores have been resized to true them up; new throttle plates machined to match; the throttle plates are installed and aligned to seal in the throttle bores and the throttle shafts are adjusted to get all three throttle plates timed to close simultaneously. Before installation I set mixture screws, idle air screws, floats and idle speed stop screws to nominal "start-up" settings which routinely results in the engine starting and idling without throttle jockying. The first adjustment I make is to achieve side-to-side air flow parity on cylinders 1 and 4 and then I check idle mixtures.
Since the carbs are "like new" mechanically and set uniformly before running the findings offered below regarding the use of Colortunes are based on a rather large amount of actual experience using a good test setup:
- None of the pre-set idle mixtures are the same after start-up so using the "I just turn the mixture screws out 2 turns" doesn't get them set correctly; use the "Lean Best" process, tail pipe readings or the Colortune. Tail pipe readings are averaged for all cylinders exhausting into that tail pipe so individual cylinder isolation is a bit muddied. Setting idle mixtures a routine number of turns out does not account for variations in: cylinder condition; inlet valve condition and setting; air leaks around throttle shafts; edge wear variations of the throttle plates; taper tolerance and centering of mixture screw in the bleed hole and bleed hole diameter tolerances to name the obvious.
- Colortune is good for getting idle mixtures set and little else unless you want to get really involved with idle jet testing in your driveway, it provides a visual indication of idle mixture where the "Lean Best" process is more artistic in its application. The settling time after mixture screw adjustment is longer than you would think, Lean Best allows one to rush the settling process where Colortune allows visual confirmation that the mixture has settled.
- any adjustment in idle air screw adjustment or throttle stop adjustment WILL affect idle mixtures
- mixture screw adjustments of plus/minus 1/8 turn from nominal ARE easy to discern with Colortune where Lean Best is more like 1/2 turn resolution
- Colortune is a fabulous tool to help diagnose individual cylinder operation, if you have an issue with a cylinder but cannot determine if you are not getting fuel or spark then the Colortune will clearly indicate which path to chase for corrective action.
Prior to involving myself with carb remanufacturing I used a Colortune to set idle mixtures on my 67S after discovering Colortune in a bike shop in 1979. I have used it to adjust all my carb'ed engines since that time, the hassle of using it is overshadowed by the positive results it provides. Again, I don't use it for more than setting idle mixtures but for multi-barreled carbs it is indispensible to me.