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MG MGA - Gunson color-tune

I pulled my spark plugs over the weekend and noticed the front ones were a nice tan color, but the rear ones were black. Using the lifting pins to check mixture was inconclusive -- both carbs sounded OK to me. So I'm thinking about buying a gunson color-tune kit to see if I can dial in the mixture a little better. Does anyone have opinions on its usefulness? The archives are silent on the issue...
Mark Lambert

Check the MGB archives. I recall reading there that the reformulated gas affects the burn color, so that the Color Tune recommendations no longer apply, or, at least, do not apply as consistently as with the "old" gas.

Regards,
M.D.
'57 Coupe
M. D.

I had a colour tune years ago and never had much luck with it. I could never make out the colours well enough to do a diagnosis.
Their carbalancer is a great tool but I never got along with the colourtune. It may have just been me though.

Rich
R.J. McKie

Mark. As M.D. notes, there is a lot of information on the ColourTune device. As Rich notes, most of us have tried it and found it of very little use. I found it completely useless for my situation--oxygenated fuel blend.

Pull the suction chambers and the pistons. Use a dial caliper to measure how low the jets are below the bridge of the carb. Inspect the needles as they are seated into the pistons. Pull the needles and read the markings on them. In one of these areas, you should find a difference which would account for your evidence.

If you do not find the problem with those invesitigations, check for an air leak around the front carb, the spacers, heat shield and cylinder head to manifold surfaces. Spraying carb cleaner around the joints while listening to the running engine is a traditional check. The sound of the engine will change as the carb cleaner makes a temporary seal around the leak.

If none above works out, check the jets for wear, they should be perfectly round in the hole the needle sits into, and check the rear needles for signs of wear.

Report back to us if you have not solved the problem and we can offer up more arcane ideas.

Les
Les Bengtson

Mark - I will fly in the face of the others. I have had a color tune for many years and it works fine for me. One thing that I have found is that it needs to be used inside or somewhere out of bright sunlight or the color washes out. Today's fuels don't give as intense a color as show on the chart that comes with the color tune, but I have found it to be useful non the less. That said, You can do just about as good a job using a vacuum gauge and adjusting the mixture on each carb for maximum vacuum. Cheers - Dave
David DuBois

Thanks for the comments. Although both carbs were rebuilt fairly recently, I can take them apart and check for various problems. The main issue for me is that I don't have any feel for the sensitivity of the jet adjusting nuts or the lift pins. It seems to me that the adjusting nut can move at least one flat in either direction without changing the engine note significantly when the lifting pin is engaged and the piston raised 1/32". And the engine note is never quite as described either. A lean note is obvious, but the difference between a rich note and a correct note seems pretty subtle to me given that I don't get an obvious rich note ("engine speed continues to increase as pin is lifted) on the carb whose plugs are sooty. And for that matter it's not clear to me how sensitive the relationship is between plug sootiness and number of flats off (the plugs are black around the gap, but not gunked up or anything). I was hoping the Gunson device would be more precise.
Mark Lambert

I tried the colortune about 17 years ago so my results may no longer apply. I ended up with the same setting whether I used the colortune or the lifting-pin method. After that, I didn't touch the carbs for about 10 years. The only reason I got into them then was to try richer needles. These carbs do not need attention unless, perhaps, you change geographic location (elevation) frequently.


Mark, maybe you want to "borrow" a colortune from a club member.

Chuck

Chuck Schaefer

Mark. As a general note, Peter Burgess recommends setting the jets .060" below the bridge in the body--that section of the lower body which is inside the throat of the carb and into which the jet is inserted. My experience is that, with both jets .053"-.055" below the bridge, the initial mixture is set properly. Almost all of the needles are .089" in the upper area (where they sit when the pistons are fully down) and then begin their taper. Thus, this initial setting seems to work well with different carb needles.

The choke can stick, allowing one, or both, jets to remain in the down position and causing excessively rich running. A check for stuck jets is always in order and this will be obvious when you remove the air cleaners and the suction chambers/pistons.

Dave is one of several people who claim to be able to use the ColourTune with good results. There have been others, whose experience I respect, who have made similar claims. I wonder if they have that "eye of the artist" which is more sensitive to colors and differences between shades than the majority of us are? I did a series of tests, about five years ago, having a number of people attempt to tune an engine using the ColourTune device. None of that test group could do particularly well. A vacuum gauge, a good quality tachometer and, best of all, a professional grade emissions analyzer all worked much better and produced a more consistant state of tune between test subjects. Ancedotal evidence, posted on these BBS's over the years, tend to support my initial conclusions. But, as with any experiment, there are always the people like Dave who seem to deviate from the average and can perform in a manner that the rest of us do not.

I have a tentative hypothesis that the people who can sucessfully use the ColorTune have eyes which can make closer gradiations between colors. I also note that many of them are experienced hobbyists and wonder if they are also using their ears when making adjustments. Are they hearing slight differences in engine sounds which provides additional feedback to their tuning? Might prove an interesting experiment for my old age. But, right now, I do not have the time to set it up properly. In the mean time, I point out that the majority of people cannot seem to use a ColourTune effectively and should one wish to invest in such a tool, one should see if it was possible to borrow one from someone and try it before investing in a personal one.

Les
Les Bengtson

I bought a ColorTune 2 weeks ago and used it for the first time with very good results.

Here's what I did:

1. Shortly after dark I went for a drive to warm the engine.
2. Pulled into the garage, installed the colortune in Cylinder #1
3. Started the engine, increased the idle speed.
4. Turned off the garage lights.
5. With garage lights off and it dark outside, I had no trouble seeing that the flame in #1 was yellow not blue.
6. With a flash light, Adjusted mixture till I got a an flame that was blue with a bit of yellow in #1 at ~1500rpm .
7. I ran the engine speed up as far as I dare (briefly) to someplace in the 3500 - 4000rpm range and noted that the flame went to a very pretty blue (like a natural gas stove flame) in that rpm range, then got more yellow (richer) at lower rpm (as one would expect with SU carbs).
8. I moved the colorTune plug to the #4 cylinder and repeated the process. I didn't have time to look at Cylinders 2 and 3.

I found the process to be surprisingly easy. For once I have some information about what's going on with the mixture, and my MGA is running better. Doing this at night in a dark garage, made it easy to see the flame color.

Hope that helps,

Steven



Steven Loe

The thing with the colortune is, you have to clean it. That sucker gets very dirty after sitting at a very rich idle for 15 minutes waiting for you to get your head out of your ar*e and figure out if counterclockwise is rich or lean.

In all seriousness, I have always had good results with the colortune. Yes, I am young and don't wear glasses. I think it's a great tool as a "rough-in" when you're installing new or rebuilt carbs or a different engine setup. It lets you dial-in very close to where you need to be. Of course, you have to balance the carbs properly first or it's useless. Once I've used the colortune to dial it in close, I take it our for a high speed run and then examine the plugs. IMO, this is your best indicator. I'll take a look at the plugs and then adjust the mixtures one flat at a time, taking test runs between adjustments, until I like the color of the plug. In my case, my car runs a bit rich at idle but at speed it's just right. I'd rather have that then normal at idle and lean at speed.

The nice thing about the colortune is that it can help you diagnose things like improperly seated or worn jets and needles or worn throttle shaft bushings. In tuning a friend's car this weekend, his front carb matched the three test results perfectly but the rear carb flashed yellow during acceleration indicating worn needles or jet bushings, which I had already suspected.

Just my 2 cents.

Mark
Mark

I bought one last week and did a ...trial test...last night. In the garage with only one light on, the combustion colour was very visible. It was so good that I could see the blue flame colour (where the spark plug tip was firing) surrounded by the yellow flame. This brought to my mind the ability to ...index ... my spark plugs. They say that helps with the combustion????

This weekend will be the real test when I do a full tune up on the engine. I feel the color tune WILL help me get the mixture right.
Thanks Gordon
Gordon Harrison

I may be able to discern fine hues of color but believe me I'm no artist! I have a color tune an like what I was able to do with it. The colors were ,to me, easily distinguished. Now where did I leave my glasses?
J.H. Hall

This thread was discussed between 02/10/2006 and 05/10/2006

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