Gunson Colortune / Experience Any Problems?

[larrym]

bettter solution - install a pair of O2 sensor plugs in your headers and buy an O2 wideband sensor kit - i did this yrs ago on my 914-6 and it will get you in the jet-choosing range at all throttle settings, on street, and on track at WOT

[1QuickS]

I use six Colortunes in my test engine for setting up carbs after I remanufacture them. When I am finished with my remanufacturing efforts the carbs have: ideal shaft/bearing fit; the throttle bores have been resized to true them up; new throttle plates machined to match; the throttle plates are installed and aligned to seal in the throttle bores and the throttle shafts are adjusted to get all three throttle plates timed to close simultaneously. Before installation I set mixture screws, idle air screws, floats and idle speed stop screws to nominal "start-up" settings which routinely results in the engine starting and idling without throttle jockying. The first adjustment I make is to achieve side-to-side air flow parity on cylinders 1 and 4 and then I check idle mixtures.

Since the carbs are "like new" mechanically and set uniformly before running the findings offered below regarding the use of Colortunes are based on a rather large amount of actual experience using a good test setup:

• None of the pre-set idle mixtures are the same after start-up so using the "I just turn the mixture screws out 2 turns" doesn't get them set correctly; use the "Lean Best" process, tail pipe readings or the Colortune. Tail pipe readings are averaged for all cylinders exhausting into that tail pipe so individual cylinder isolation is a bit muddied. Setting idle mixtures a routine number of turns out does not account for variations in: cylinder condition; inlet valve condition and setting; air leaks around throttle shafts; edge wear variations of the throttle plates; taper tolerance and centering of mixture screw in the bleed hole and bleed hole diameter tolerances to name the obvious.
• Colortune is good for getting idle mixtures set and little else unless you want to get really involved with idle jet testing in your driveway, it provides a visual indication of idle mixture where the "Lean Best" process is more artistic in its application. The settling time after mixture screw adjustment is longer than you would think, Lean Best allows one to rush the settling process where Colortune allows visual confirmation that the mixture has settled.
• any adjustment in idle air screw adjustment or throttle stop adjustment WILL affect idle mixtures
• mixture screw adjustments of plus/minus 1/8 turn from nominal ARE easy to discern with Colortune where Lean Best is more like 1/2 turn resolution
• Colortune is a fabulous tool to help diagnose individual cylinder operation, if you have an issue with a cylinder but cannot determine if you are not getting fuel or spark then the Colortune will clearly indicate which path to chase for corrective action.

Prior to involving myself with carb remanufacturing I used a Colortune to set idle mixtures on my 67S after discovering Colortune in a bike shop in 1979. I have used it to adjust all my carb'ed engines since that time, the hassle of using it is overshadowed by the positive results it provides. Again, I don't use it for more than setting idle mixtures but for multi-barreled carbs it is indispensible to me.

[rbogh901]

Originally Posted by haycait911

I tuned my mixture on webers and a 3.0 with a colortune a couple of months ago. went for orange burn with blue streaks, I like it a bit rich. pulled the plugs the other day. I'm no expert but they look like perfect burn to me.

I like the unit, grounding/shocks were a pain at first but I figured it out. for $60 it's tough to beat. it's like a lot of diagnostic tools, you really need all the engine systems in good shape and working properly for it to be useful.

Don, it's been a while but this is a useful thread. I understand the value of interrogating individual cylinders and their respective idle circuits and am going to see how close my lean best tuning got me by comparing with a Colortune. My guess is that I am, in fact, lean.

Are the grounding shocks from positioning the mirror? Do you have tips for installing/removing the unit?

[haycait911]

I forget just where I was getting shocked. I 'm sure you'll find out

for install/remove, be gentle. it doesn't need to be torqued down. just seat it lightly and go to town. be very sure your idles jets are absolutely clean first. on each cylinder I adjust idle mixture, pull the idle jet and blow it out, look thru it, re-install and re-check with the gunson. a bit of transient schmootch in the jet can really throw you off. I wound up using around mirror on a telescoping rod to look. much easier to get the angle than the attached one.

[rbogh901]

Yes, agreed, I clean my idle jets. Blow them out and shoot 'em with carb cleaner. I never see anything in them and it never makes a difference but I'm always paranoid that there might be some tiny little smudge I'm missing so I do it anyway.

Do you find that adjusting one barrel effects the others sufficiently that you have to go around twice to get the best results? I know Paul uses 6 at once so he doesn't have that problem.

[florio]

I'll add my 0.02$ worth, I have two colortunes and use them to balance the twin webers DNCF 40 on a V6 in the 'other' car. I move them in pairs on each of the three carbs and the system works great. The color is very responsive to the mixture at idle, and this helps avoid running the idle rich (which eventually leads to fouling of your plugs). But, access and clearance is much better than in the 911.

Dario

[1QuickS]

My site (active link below) provides info regarding use of Colortunes and some "Tips" also; most important "Tip" is to tape a quarter to the plastic tube & throw it into the trash so you can say you threw something away that had some value.

Performance Oriented

[rbogh901]

In an effort to clarify for those who might follow:

Here is a photo of the plastic tube and cheap silvered "mirror" referred to circled in red that apparently has little use for us per Mr. Abbot et al. Also note the spark plug proxy circled in blue. It, and the minimally insulated lead wire in the foreground, form the real investment/excitement here apparently. Maybe more insulation could be applied to decrease the excitement factor?

[matthewb0051]

Originally Posted by Traveller

If you can.

Yep, removal is the problem. Tight space, hot engine, ooops droped it in the spark plug hole...

[1QuickS]

Magnet on a wand will retrieve them but my go-to tool is a pair of curved forceps.

[rbogh901]

Had a go for fun on just one cylinder to see what we are up against and it's very nice to see 1/8 turn impact the combustion so obviously, once you see the thing down that hole. Still, once you see it there it is. I did number 4 as it's the easiest to access. No way I would ever be able to audibly discern that kind of difference from the background of 5 other cylinders firing and misfiring as the case may be. And approximately 1/2 turn out from stumbles is way too vague comparatively.

Don has a good point when he mentions that going gentle is enough. It only takes a minute to get the color pretty dialed once you see it and it's done at 900-1000 rpm idle after side to side balancing.

[rbogh901]

I'm sure everyone has their own method of doing this. I've sorted it out to the point where I'm fine installing, removing, and tuning but the hardest thing is getting a good sighting down the plug hole. I'm using a small 3/4" electronics mirror on a rod and once I get a solid look there's no problem but it takes some fiddling, maybe a different one would be better. Do you have suggestions on mirror and placement?