Using a gunson to set mixture

Any thoughts or experience using a gunson color tune on your e type. Thinking it would be nice to set mixture with the air filter in place.

I use a Heathkit exhaust gas analyzer that I built 40 mumble years ago. It still works and is great for setting mixture on any car it does not have a catalytic converter. There are probably a number of old exhaust gas analyzer’s on eBay. If you go that route, be sure you get all the parts. The last one I saw for sale didn’t include the sensor. The person selling it was clueless and didn’t mention that it was missing unobtainable parts.

I have used it to set mixture on the ZS carbs with adjustable needles on my '68 E-type. Also on my dual Weber DCOE’s on my Cosworth Vega. Pretty straight forward for me following the directions that came with my Color Tune kit. I set mine to show mainly blue flame with flecks of orange (yellow) to be a little bit rich. My main concern was not to set things too lean.

68 E-type FHC

Those are suppose to be pretty decent units.

I’ve got a tester made by Hawk that is probably about as old and seems to work. I prefer, though, to set the carbs with the Colortune and listening to the exhaust for a regular or irregular “sputting” which indicates lean or rich carbs.

I too have the occasional sputting, but can’t figure out whether I’m too rich or too lean. I suspect lean so I am richening it and test driving, richening it and test driving it. It’s still pops on the overrun. My problem is that I’m running a non-standard carburetion set up of two HD8 on a 1970 manifold that was originally designed for 1.75” stralnglebergs.

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According to the driver’s handbook:

When the mixture is correct , the exhaust note should be regular and even. If it irregular with a splashy type of misfire and colourless exhaust, the mixture is too weak. If there is a regular or rhythmical type of misfire in the exhaust beat together with a blackish exhaust, then the mixture is too rich.

On carbs set up for proper all-around running, you’re not going to get rid of overrun back-popping: it’s a feature.


You can minimize it, but I never got rid of it completely.

The information in the manual about detecting rich/lean is essentially prehistoric. I’m not saying that it is wrong, just that there are much better objective tuning aids now available.

Similarly with unleaded fuels plug colour and exhaust pipe colour are no longer much use as everything looks black until you are way too lean.

I have tried the Colourtunes and not had much success, although others swear by them.

I have a Gunson CO analyser G4125. I set the CO at about 4.5 to 5.5% and all my cars run beautifully. In my view, given the complexity of the 3 carbs into 2 exhaust manifold setup this is the only way to go.

I use a Colourtune and it produces better results than I have managed any other way. I first set the air on each carb using a UniSyn and then work through each cylinder pair with the Colourtune. Some of us use three Colourtunes simultaneously. I find the car is happiest about 1/2 a turn richer than the blue flame indicates. Needless to say all the linkages and choke “pulls” have to be correct along with ignition timing. Car has Rock steady idle with the choke on or off. Paul.

Thanks for that Paul.

I’ve still got mine in the shed. I’m going to plug it into one of my cars and see what it looks like.

For my two Strombergs (adjustable TR4 jets) I use a pair of Colortunes - gets a good result.

Oddly, even though Gunson is a British company, the product is spelled without a ‘u’:

A digital camera can preserve the results:

Colortune Flame

But use a telephoto lens - you do not want to get a digital camera close to a spark plug wire (as I discovered).

Did you, the camera, or both suffer the consequences? :laughing:

Both I and the camera survived w/o lasting impairment - but there was a zap and the resulting photo was not so good.

True. I suspect the factory didn’t expect the average owner to have much in the way of sophisticated shop tools at their disposal.

You are correct. I just had a lapse and reverted to type.

Using a hose to balance air intake is much handier and just as accurate. Could not find the uni syn . so I grabbed a sounding hose and found it to be the better tool

The ColourTune is useful for quickly getting to a good, consistent starting point for setting mixture. It is useless for setting final mixture, because there is no defined correlation between idle mixture and at-speed and at-load mixture, both of which are FAR more important to get right.

Do the following, for one cylinder of each pair (1-2, 3-4, 5-6) with SUs, or each triplet (1-2-3, 4-5-6) with S-Zs:

  1. Install the ColourTune, start the engine, let it run at a full-temperature hot idle.
  2. Adjust mixture to where the color is JUST on the edge of where it changes between yellow and blue, preferring the yellow side.

This will get all carbs to a common mixture point. Now go drive it, and make any adjustments in equal increments on ALL mixture screws. If you get lean surge at cruise, go richer in 1/4 turn increments on ALL mixture screws, and re-test, until it goes away, or some other undesirable symptom appears. If you’re getting excessive popping on over-run, go leaner in 1/4 turn increments on ALL mixture screws, and re-test, until it goes away, or some other undesirable symptom appears.

Ray L.

I’ve read conflicting information on popping and overrun. Do you go leaner as you stated or richer?

overrun is dieseling?

Could be either, but too rich is more often than not the cause. The popping is caused by un-burnt fuel igniting in the exhaust system.

Ray L.