Britbike forum Forums Thread Like Summary - Any experience with Gunson Colortune?

I just purchased one of these, a G4074, for "vehicles with 14mm spark plug". It came with a "short reach" plug, but I see in the documentation that there is also available a 14mm "long reach" plug. Does anyone know which is correct or more appropriate for an A65?

Also, although not spelled out in the documentation, it appears that the use of the "viewing tube" is optional, perhaps only required where you cannot get a clear view of the spark plug. (The viewing tube has a mirror on the end, placed at an angle to the tube.)

Love the colour Tune. Great for getting the idle mixture right with a new carb. Also checking spark on cylinder. On the BMW with its Bing carbs as you crack the carbs open you would see the mixture turn yellow from blue at idle. Then as it came up to speed and leveled off the CV carbs would return to blue. I have never seen this with an AMAL MK1. It always stays rich. (yellow) Of course at higher rpms it was no load as I never had the guts to ride the bike in the dark while staring down at the colour tune. Seemed like a good way to drive off into the trees. After idle I'm looking for Tan on the insulators of the Plugs to set the needles. WOT plug chops to set the mains.

The blue has a range 1/8 - 1/4 turn on the air screw. Setting on blue towards the lean side if you like the pop from you exhausts as you close the throttle to a stop. Set it toward the rich end of blue if you don't.

Colour Tune gives you information you wouldn't normally have. What you do with it is up to you.

Save your money and don’t bother.

The colour tune is only going to give you a decent reading at idle. Unless the motor is properly heat soaked then what ever you set it to won’t make any difference. You can set the idle easily by adjusting the mixture screw until it gives the fastest tick over then screw it in a gnats hair.

Off idle the mixture should be richer.

Ride the bike and make adjustments from there.

Even if you don’t use it for tuning it’s a useful tool for training your ears. Watch the colour change and listen to the engine. Once everything is heat soaked you may well notice the difference in the way the motor idles and you have a bench mark for any further mixture adjustment.

I own two!

I see the Colortune as an interesting toy. Something for a school demonstration.

Any time I set the mixture with a Colortune (or two!), I had to correct it afterwards.

They are also extremely useful for diagnosing those fuel problems where, just coincidentally, there is no spark.

I always use mine after a ride, unless the engine is up to temp the readings are meaningless. As stated, it's really only for idle settings. However, it should read rich when you blip the throttle so it can be used to check your slide cutaway. Should go rich then return to correct when held at 2-3000rpm.
I've never used the viewing extension. Might be handy on the center cylinder of a triple though.

With idle stabilisation curves on the digital ignitions a colortune is now a must. Doing it by ear no longer works as with idle stabilisation, as the revs drop the spark is advanced to recover the revs, so doing it by ear is out, the colortune shows you when the mixture is right regardless of the revs. If you have no idle stabilisation then by ear is just as good or better but it will tell you if the spark is good or not.

Color tune as seen by aircraft mechanics, so just cut off them pipes

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ive used a colortune for decades. they only work at idle and slide cutaway, but thats what theyre for--any great cylinder pressure will blow the little mica window out, i imagine. i have an AEM AF gauge that i use for larger throttle openings when im tuning something from scratch. but even the AF gauge isnt as good as a simple stopwatch. +

at idle, i find that i can get a much finer tuning using my eyes than using my ears, and i have also found the colortune useful for diagnosing manifold air leaks as well as for selecting between pilot jets. theres nothing wrong with tuning by ear if you re good at it, but i have always learned more and gotten better results by using instrumentation that lets me actually measure and compare things.

rich

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lean

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Short pipes? Yeah, that'll give you an accurate mixture reading for when you put the whole system back on.