Gunson Colortune, Am I using it wrong?

[danny01975]

So I got a gunson colortune. Figured it would be a good buy and I could share it with my friends who also have vintage Japanese bikes. I followed the instructions and watched a few videos, all basic stuff. It ain't rocket surgery.

But what I noticed is the range of adjustment for the "bunson blue" color is huge. The bike idles differently at 1.5 tuns, 2 turns, 2.5, turns and almost 3 turns, which is where it seems to run best. All of these settings produces a nice blue color. The only way really to get it white or orange is to turn the adjustment screw nearly all the way in or out. Rendering the tool nearly useless.

It just seems the resolution of the tool isn't fine enough to produce any meaningful measurements. I'm better off using the ear method it seems. Am I doing something wrong here?

[Grimly]

Gunson's Colortune was designed to work with the SU carb, which only has one jet, no supplemental idle or other jets (apart from a starting jet on some models). This makes it a reasonably reliable device on SUs. It was designed to cater for standard jetting, so that the idle position was a good enough guide to what would be happening further up the rev range, as it was all sorted out at the factory in advance.

I've had some success with it on my XJ900F carbs which are Hitachis, but I did notice the bunsen blue range was wider than I expected, because of the above. The Hitachis are similar to the Mikunis in having other jetting that adds to the soup. Other owners of other XJ models seem to find it works well enough for them, too. Having said that, there's a mix of carbs fitted to XJs, so <shrug> .

[zed1015]

Colour tunes are good for old ford cortinas otherwise leave it in the box..

[Brendan W]

It sounded like a great idea when I bought it in '83 and it is cool to be able to look into the cylinder.
The novelty wore off fairly quick as I could never get it to do something useful or repeatable.
Put it down to my inexperience and went back to plug colour, exhaust colour, smell and fuel consumption.
It's in the same box as that dwell meter.

[danny01975]

It sounded like a great idea when I bought it in '83 and it is cool to be able to look into the cylinder.
The novelty wore off fairly quick as I could never get it to do something useful or repeatable.
Put it down to my inexperience and went back to plug colour, exhaust colour, smell and fuel consumption.
It's in the same box as that dwell meter.

Sounds like my experience exactly. I think I'll just sell it on eBay.

[oldGSfan]

I acquired one with a Suzuki and tried on my '66 Norton. I got it to the color range per the instructions easily but it didn't run as well as it did before I adjusted it. I just have one Mikuni VM34 on the bike. I asked on the Norton forum and folks said that's exactly what will happen - you can do better by the standard Mikuni tuning method (on that carb anyway), listening for idle drop. I had mine spot on and put back to the setting and all's good. I think my earball adjustment method landed it just into the blue with no yellow at all, so about 1/8 turn leaner, as I recall.