At the request of a member on this forum (no names mentioned), I'd like to relate my experience with the following product in an attempt that you'll avoid the grief.
Colortune Product Warning
If you are considering the purchase of a Colortune Carburetor Tuning Aid, you might want to reconsider.
I originally saw this product advertised in the BMW MOA Owner's News by Bing Agency International (BAI). They claim that this product enables you to "adjust your carburetors precisely". It does so by providing you with what is essentially a spark plug with a transparent insulator. The transparent insulator enables you to see the color of the combustion while carburetor adjustments are made. This is much like adjusting the color of the flame of an oxy-acetylene torch.
The principle of operation is not the reason for the warning although I have added a few comments regarding this at the end.
The Colortune that I received did not meet the "SAE" or "Revised British" specifications for spark plug dimensioning. Unfortunately I wasn't aware of this until it was too late. The Colortune, although threaded in by hand before lightly tightening, was difficult to remove from the cylinder head of my BMW. Luckily only very minor damage resulted. I took the COLORTUNE along with two randomly selected spark plugs to work for dimensioning. The BOSCH was dead centered within the SAE spec and the NGK was towards the lower end.
The major diameter of the Colortune (0.5498") was greater than the maximum set out by the "SAE" and "Revised British" Standards. I brought this to the attention of both BAI and Gunson, the manufacturer in England. Gunson claimed that the measurement that I provided them with fell right within THEIR tolerances of 0.5455" to 0.5505". Sure enough it does; unfortunately THEIR tolerances didn't coincide with neither the "SAE" or "Revised British" standards. I questioned Gunson as to the source of their standard but no response as of yet.
As for the Colortune, I can say that it would've made an expensive paperweight if I hadn't been offered a refund. As far as using the Colortune to set up carburetors ‘«£precisely‘«ō; forget about it. Set them up using the manufacturers recommendations and then make final adjustments (which the Colortune couldn‘«÷t do in any case), on your own. Makes me wonder if BAI or Gunson know the definition of the word "precisely". Additional information may be found in the 23rd edition of the Machinery Handbook.
The BMW MOA directors were informed of the problems I experienced shortly after I purchased this product in 1992. Although one director took the time to look into my problem, I was basically ignored by the BMW MOA. Their tech expert that contributed to the monthly magazine in the past, took my side and agreed with my findings. More recently (2000), one of the directors looked into the matter only to inform me that a sample that he received measured within tolerance. I‘«÷m not arguing his findings. The FACT that MY unit didn‘«÷t meet specifications requires that BAI and GUNSON come good for damages to my motorcycle due to the use of their ‘«£totally useless‘«ō product.
If you choose to use this bogus product, do yourself a favor and measure the major diameter of the threads to see it they indeed are within specifications. If they do meet specifications, you‘«÷ll still be using a product of questionable use.
As a 12 year member of the BMW MOA, I'll add that I take any product evaluations in the Owners News very lightly and more of a "trumpet blowing' session. For any product evaluation to be unbiased, especially if the product is advertized within the pages of the Owners News, it would have to be done by a person that provides a write-up of all pros and cons of the product. Most of the time, I just see the pros.