Gunson Colortune Opinions

[Guest]

Anyone have any experience with a colortune? Thinking of buying one to tune my 83 GL650 carbs.

https://www.ebay.com/itm/Gunson-G4171-Colortune-Single-Plug-Kit-Motorcycles-with-12mm-Spark-Plug/222582530328?epid=5005471751&hash=item33d2f3e118:g:ObwAAOSw2XFUapN2:rk:3:pf:0

[niclpnut]

Can help find optimal idle mixture.

Like it on the 2 valve motors, but not do much on 4 valve.

Nic

[fixmybrokecomputer]

What's the difference?

[Steve]

I have not noticed any difference between 2-valve and 4-valve engines, but I have definitely noticed a difference with the CV-type carbs, which I believe your GL650 has. By the way, yes, I did notice that it's a GL650, not a 650GL, which is normally found on this site.

I used on on a set of early VM carbs and was very pleased. Based on that experience, I borrowed the unit to see how it would work on our bikes, which are all newer, with the BS series CV-style carbs. On the VMs, you could see the color change with every little twist of the air screw. On the BS carbs, turning the pilot screw (some also call it the mixture screw) showed absolutely NO change in color. As the mixture was leaned out, the flame started dropping out, but never changed color. Eventually, the flame stopped completely. As the screw was turned out to richen the mixture, the flame started popping to life again, eventually getting steady. As the screw was turned even farther, the color never changed. Several others here have noticed the same thing. Not sure if it would be any different with your (Kehin?) carbs.

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[fixmybrokecomputer]

Thanks for the explanation Steve. Any idea why they behave the way they do on CV's?

[Skinner]

I'll chime in as someone who has experienced the opposite of Steve. Not discounting Steve's experiences at all, because several others have also reported the same results as him. That said, I had a GS650GL and currently have a GSX750S Katana, both 4 cylinder bikes with CV carbs. I've had great success with the Colortune. Adjusting the mixture screw results in obvious colour changes from blue to yellow with the corresponding change in idle. I've been able to dial in my carbs quite easily with this device - I'm quite happy with it.

Cheers!

[Steve]

I'll chime in as someone who has experienced the opposite of Steve. Not discounting Steve's experiences at all, because several others have also reported the same results as him. ... - I'm quite happy with it.

Nice to hear from someone with a better experience.

I have seen a few other "success" stories, I might even start looking for a Colortune to add to the shop's arsenal.

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[Grimly]

Well, given the Colortune was developed for the SU-dominated car market of the UK in the 60s, it might reasonably be expected to work with just about anything similar.
However, I'm not surprised that some carbs defeat it, especially some of the closely-designed CV carbs coming out of Japan in the 70s and 80s.
Having said that, my experience of them is this - SUs - fine; most other fixed-choke carbs - fine (at least it tells you if you're a mile out or bang on, even if you can't do much to adjust some of them).
The Hitachis on the XJ respond well to it, but only for the idle tune, as you would expect.
The Colortune is a device which takes for granted you're still using the manufacturer's needle and jets for anything above idle, so ideally when you set the idle right, the rest of the fuelling range should come right, too. This is especially the case in the likes of an SU - if left unaltered from factory specs, the idle condition will pretty much bear a relationship to the rest of the fuelling range.
That's not always the case, and if things have deviated from the norm, you might not be able to make sense of the colour changes, unless you know exactly what was done and what to expect.
I'd definitely always have one to hand, because although you might not be able to rectify the problem, the thing will tell you what the problem might be.
In short, they're a very useful diagnostic and setting-up tool, but of course they have their limitations.

[fixmybrokecomputer]

Good discussion! Thanks to all for the contributions to this thread. I appreciate all of you very much! Keep the posts coming.

[Righty]

I just used colortune on my 1980 GS550 over the weekend. The previous owner put in pilot and main jets that were way too big for the bike. I experimented with different sized pilot jets and the flames were constantly orange the whole time no matter how much I adjusted it. This means the jets were too big and needed smaller ones. Once I installed a jet that turned the flame blue when adjusted, it took a total of 10-15 mins to get the rest dialed in. Bike runs like new now.

[fixmybrokecomputer]

I just used colortune on my 1980 GS550 over the weekend. The previous owner put in pilot and main jets that were way too big for the bike. I experimented with different sized pilot jets and the flames were constantly orange the whole time no matter how much I adjusted it. This means the jets were too big and needed smaller ones. Once I installed a jet that turned the flame blue when adjusted, it took a total of 10-15 mins to get the rest dialed in. Bike runs like new now.

Thanks for sharing your experience!