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Color Tune

From Listserv Digest 2593 May 7, 2001  ( See update from Harry Martin below )
From: "Darren Fuerst"

Every now and then I mention using the Colortune to set Connie's idle mixture screws, and every time I do so I get backchannel requests for more  info.  I thought I'd pull together the various bits and pieces, and create the:

Connie and the Colortune Mini FAQ

Opening Thoughts
Ok, all together now, let's say the DIY mechanic's chant: "IF IT AIN'T BROKE, DON'T FIX IT!".

Every so often I see advice to new Connie owners that they should set their  mixture screws X-turns out (insert your favorite number in place of X). The bike will run smoother, pull wheelies in 5th, spank ZX11s, get 100 mpg, add inches to your...I digress. This advice is, unfortunately, not true for most owners.  If your bike starts and idles fine, doesn't foul plugs at idle/low speed running, and pulls smoothly off idle, then futzing with the mixture screws will almost certainly make it run worse, not better.  This is especially true for newer/lower mileage bikes.  The mixture screws were adjusted at the factory, and (provided that it was done right, and it probably was) will provide the best balance between performance and emissions. 

If you need to fondle Connie, and Coggers really do love to tinker with their scoots, leave the mixture screws alone and do something useful instead.  Change the oil, or the brake fluid, or clean the air filter, or you could even (*gasp*), wash it.  If you really want to play with the carbs, try shimming the needles, which really will produce an improvement in performance and drivability with much less work and risk, or try leaner main jets. Repeat, now, FUTZING WITH THE MIXTURE SCREWS ON MY BIKE WILL LIKELY MAKE IT RUN WORSE.

On the other hand, there are situations in which adjusting the mixture screws is necessary.  Maybe you have an old/high mileage bike.  Carbs are mechanical devices, and do  wear over time.  Vibration hammers moving parts together,  fuel moving at high speed is errosive over time, and adjustments can drift.  You might have a used scoot that the previous owner or a previous mechanic "tuned".  (For example, on my used 86, the PO or a mechanic had left out the little washer on the pilot screw of #2, and installed it -- doubled up -- on #1.  Weird.)  You might be replacing a physically damaged carb with a new or used one.  Perhaps your mixture screws were set at the factory by a worker who drank his lunch, was just dumped by his wife, and was suffering through a pesky hemorrhoid flare-up.  Maybe (like me) you do a lot of cold-weather riding, and cold-start ease and drivability are important.  In these situations, some adjustment of the mixture screws may be called for. Mixture screws are fairly easy to adjust on singles and twins; adjusting them on a four cylinder bike, however, can't be done properly without some special equipment.  The "X-turns out" method (i.e., setting all mixture screws 2 turns, or 1.5 turns, or whatever, out) is really a "limp-home" deal only.  Yeah, the bike'll start and idle, but performance will not be optimal, and the emissions will certainly be higher than necessary. 

The best method for setting mixtures is an exhaust gas analyzer (EGA). Although you can buy relatively inexpensive EGAs for home use, they're still mighty costly for us average folks (considering how often you're likely to use it), and you may need to weld in special bungs on the exhaust headers for the sensor.

What is the Colortune?
The Colortune is a sparkplug that takes the guesswork out of setting mixture screws, and it's a hell of a lot cheaper than an EGA. The theory behind the Colortune is quite simple.  Mixtures with differing fuel/air ratios will burn with different colors.  You already know this, if you've ever adjusted a gas burner, Bunsen burner, welding torch, whatever. Rich mixtures burn yellow or orange, whereas mixtures with the correct fuel/air ratio will burn a bright blue.  Wouldn't it be nice if you could peek inside the combustion chamber of a running engine to look at the flame color as you tweak the mixture screws? With the Colortune, you can.  The Colortune is a sparkplug with a transparent window that lets you observe the flame color in a running engine.  The basic operation is quite simple.  With the engine running, turn the mixture screw out until you obtain a yellow flame (rich).  Then, turn the mixture screw in until the flame just turns blue.  This is the correct mixture screw setting for best performance.  Obviously, this is repeated for all cylinders.

The Colortune can be ordered from Eastwood Co. (  The current price (May 2001) is $49.99.  You'll also need the 12mm adaptor, which is $8.99.  Search around, you may be able to find it cheaper.  (Ok, I just tried taking  my own advice, and found it $10 cheaper at  I bought mine quite a few years ago, and paid around $30, IIRC.)

The Kit
The kit contains the Colortune plug itself, a "viewerscope" with an adjustable mirror that makes it easier to see the plug from weird angles, an extension HT lead, a copper sealing washer, a cleaning brush, and cleaning solution.  The 12mm adaptor comes with a 12mm sealing washer.  There's also a pretty detailed instruction sheet with use and troubleshooting details.

Although the Colortune is pretty idiot-proof, as always, the devil's in the details.  The Colortune is not all that easy to use on the Connie, because the plug wells are deep, and getting at the #2 and #3 plugs is not easy. The manual covers all the basics of using the Colortune, so I'll just concentrate on Connie caveats.

First, you'll need some method of adjusting the pilot screws with the carbs in place and the engine running.  Obviously, you'll need to remove the anti-tamper plugs that hide the mixture screws if they are still fitted on your bike.  Depending on the tools at your disposal, this may require removing the carbs, which is not fun, but can be done with ordinary hand tools, a lot of silicone spray, and a lot of swearing.  The procedure is described in detail in BOC.  Craig Stiniker [] has posted instructions on the listerv for removing the antitamper plugs with a Dremel tool, with the carbs in situ.  Keep in mind that when the carbs are on the bike, there's precious little room to get a screwdriver under the carbs and onto the mixture screws.  A small slot-head screwdriver with a cut down handle will work.  There's also a special tool designed for exactly this purpose (a right-angle screwdriver) made by, I believe, Motion Pro (I could be wrong about this, again, I bought mine quite a while ago) and available from many MC mail-order houses.  I've used both.  The special screwdriver works well, but is not necessary.

Second, you'll need some sort of fuel supply, since the tank will need to be removed throughout the process (just like when you're synching the carbs). Some people like to use an auxiliary fuel tank.  I just set my tank on a utility cart beside the bike, and run a long fuel line to the carbs.  With the tank off you'll need to plug the vacuum line to the petcock (I just use a screw of appropriate size) or plug the vacuum port at the #2 intake manifold), and run the petcock on Prime.

Third, the mixtures must be set with the engine at normal operating temperature.  YOU WILL NEED TO WEAR GLOVES TO AVOID BURNS.  The engine will be hot, and the Colortune plug (and the regular sparkplugs) will be VERY VERY HOT.  If you're not careful, you can give yourself a rather nasty burn or two.  You have been warned.

Fourth, the sealing washer for the Colortune plug is not captured to the plug body as it is with a regular sparkplug.  This is the biggest PITA when using the Colortune on a Connie.  When fitting the Colortune, you must drop the sealing washer into the plug well first, then use a flashlight and pick or long thin screwdriver to jiggery-poke the sealing washer flat against the head before fitting the Colortune.  When you remove the Colortune, you need to fish the sealing washer back out.  This is a real pain on cylinders 2 and 3, where access is very limited.

Fifth, because the plug wells are deep (and hard to get at on 2 and 3), and the sealing washer is not part of the plug, it can be difficult to get the Colortune plug screwed in.  I've found that the easiest method is to fit the HT extension lead to the Colortune, and use the lead to get the plug positioned straight in the plug hole and the threads started.  Once started, the viewer scope can be used to screw the plug in the rest of the way.  The Colortune should only be fit finger-tight -- just enough to get a gas-tight seal.  Don't leave the viewerscope in place -- it's not really necessary on the Connie, and you could wind up melting it.

Once fit, setting the mixture screw is straightforward.  The manual warns that the Colortune is hotter than a normal plug to prevent fouling of the window.  Once the engine's running, it's a good idea to get the mixture screw set with some dispatch.  Don't run off to answer the phone or get more beer while the engine's running (that's what spouses are for).

Closing Thoughts
My own experience with the Colortune has been very favorable, and this is the third bike that I've used it on.  YMMV, of course.  As you'll likely not need to set mixture screws very often (you should be able to set 'em and forget 'em for quite a long time), you might want to split the cost of the Colortune with other friends that ride and wrench.  One lister has reported that he tried the Colortune once, but was unable to get the mixture screws out far enough to get the rich (yellow) flame color.  For the life of me, I can't figure out why this might happen, and no one else (that I know of) has had this problem, but it bears mentioning.  I've found that on my bike, at the "limp home" 2 turns out, all the carbs are running too rich already.

Dec. 21, 2003 
From: Harry Martin

Just a quick report on the "motorcycle" version of the Colortune.

I finally got my carbs reinstalled after a good cleaning and replacing one float valve. To tune my carbs, I decided to purchase the Motorcycle Colortune 4168 instead of the standard 4074. This version is the 12mm model that does
not require an adapter to make it fit to the Connie.  From the manual..."This model has a smaller internal volume (which
maintains the normal compression ratio) and a higher heat range, more suited to high performance engines."

Well, I don't know if it make a difference or not, but I used it and it worked just like the manual says.

Some points to consider before using it.

1. I found that the whole process was very easy to do if you remove both coils and move them back towards the rear. Easier to do if you upgraded your sparkplug wires with a Murphs wire kit as the extra lengths I added allowed me to move the coils out of the way. The engine still runs fine with the coils not bolted down.

2. As a right handed person, I found the #2 Carb pilot screw the most difficult to adjust. In the future, I will start by adjusting that one first and then progress to the easier ones.

3. A short hex bit screwdriver works well to adjust the pilot screws, except for the #2 carb since the alternator tends to be a tad bit in the way. Takes a bit more fiddling, but can be done. I can see where a knurled knob added to the screwdriver bit would be a big plus, but I managed without it.

4. Make a wire loop to fish out the washer after you remove the Colortune. It's easy to fish out.

5. If the Colortune will not back out using the supplied plug extension wire, a 5/8" plug socket will do the trick.

6. Install the Colortune no more than finger tight!

It was fun and easy to use. The price of the Colortune more than paid for itself and I expect to see an improvement in gas milage. My carbs were running extreamly rich. The smell of hydrocarbons is now gone. When I first looked through the clear window to watch the combustion, each cylinder was showing a bright orange flame. Now they all show the proper blue color of correct air fuel mixture. I followed up the carb tune with a carb resync using my lethal mercury carb sticks. Everything is now copecetic.

Today, I braved the balmy 65 degree weather with my summer jacket and gloves and took her for a test run. Now, acceleration is *real sweet* from idle to redline.  I can accelerate faster than I can hold on.

There are other accessories in the Colortune kit. I didn't need any of them. It's plently dark enough in the sparkplug well to see the flames and enough shade in the garage (even with the door open) to easily get the job done. The user manual is well written and contains 2 pages of  symptoms/Fault details for easy troubleshooting.


    Gunson Colortune
    Murphs plug wire kit
    Murphs carb screw kit

This tool has earned its keep and is small enough to take on the road. The advice that 2 turns on the pilot screws will get you home - is nice, but this gadget will get you home in style. My 86' Connie now runs a lot


Article By: Darren Fuerst

Updated September 2007

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