I’ve seen reports of diy’ers using this product to fine-tune the idle rpm mixture, mostly on carbureted engines. It apparently allows you to actually look inside the cylinder as the engine runs, and you adjust the mixture to get a nice blue-looking flame, like if you were adjusting your natural gas stove. Does anyone here have any experience with this product? It seems like a good idea, but maybe there are some impracticalities?
It’s been around for decades. You can find out how to use it on YouTube.
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I used to use those perhaps 55 years ago. While it worked nicely, I found I could get just as good an idle using my tach and a vacuum gauge, and it was quicker. I think I got it from J.C. Whitney
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That’s how I do it now. I get a good idle in the sense that the engine idles smoothly even though I’ve adjusted the adjustment toward lean as much as possible. but I don’t really know if the idle mixture is correct or not. I tend to end up with the mixture adj screws 2 1/2 turns out, and some books saying 1 1/2 turns out is closer to correct mixture.
Don’t remember how I adjusted the carbs on the corvair but think I just used a vacuum gauge.
I would start with 1 1/2 turns out, and then adjust in or out to obtain the highest vacuum reading. I was never concerned if the mixture was stoichiometrically “correct” as long as i had a smooth steady idle at 550 rpm in drive.
I’d just adjust for leanest smooth low idle.
Good grief . . . ! 
I haven’t heard anybody mention colortune spark plugs in DECADES 
I’ve still got an old jc Whitney catalog. It’s fun to go through it sometimes just to see all the products like the pellets to bring back a dead battery. Never heard of those spark plugs though. Don’t know why I should have.
I don’t think Gunson is an American company . . . at least it doesn’t currently seem to be
And their products are . . . for the most part . . . not professional quality, imo
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I’ve never heard of them either and I have to very good friends that are in there mid 70’s with lots of old school tools and we have done a lot of tunning together and they have never mentioned to me nor used one around me, and I new there tool boxes very well… Not saying they never had or used one, just not that I saw or heard of…
It sounds a lot like snake oil to me… lol
I used color tune on many dual SU carb 4 cylinder engines many years ago.
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