Gunson Colortune

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Philk
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#1 Gunson Colortune

Post by Philk » Tue Dec 18, 2018 11:11 am

Hi all

I'm considering getting a Gunson Colortune. Having downloaded and looked at the instructions, I can see that Gunson recommend buying a colortune per carburettor so you can adjust each to near identical behaviour (as the colour goes from yellow to blue). Has anyone purchased multiple units to use on their "E"s? In one respect it sounds like good sales patter but also sounds to make some sense and, presumably, would be less hassle than moving one from carb to carb and possibly back again.

Thoughts most welcome (as would be any up to date feedback on the Colortune product itself).

Thanks

Phil
Phil
1964 S1 3.8 OTS

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phil.dobson@mac.com
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#2 Re: Gunson Colortune

Post by phil.dobson@mac.com » Tue Dec 18, 2018 2:55 pm

I like them. I have two and use them for the initial settings. If you take your time they can give you a very good result. you can see what a 1/4 turn of the mixture screw can do. be patient when using them and you will get good results. Like all tuning however the starting assumption is that all systems are in reasonable condition, especially the ignition and timing

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christopher storey
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#3 Re: Gunson Colortune

Post by christopher storey » Tue Dec 18, 2018 3:55 pm

:yeahthat: I second what Phil has said

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malcolm
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#4 Re: Gunson Colortune

Post by malcolm » Tue Dec 18, 2018 5:17 pm

I use a single Gunson, to good effect, but you should be aware that E's like to run richer than the colortune would want you to set it too!! I got everything lovely and blue, and it ran like a pig. I found you need to get each cylinder so that it just turns blue then richen it up a quarter turn.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#5 Re: Gunson Colortune

Post by christopher storey » Tue Dec 18, 2018 6:40 pm

Again, I agree with Malcolm : XKs run best at a stoichiometric ratio of about 12.5 : 1 rather than the ideal ( weaker) 14 or so, and this equates in flame colour to what I would describe as a mixed yellow/blue flame. It's some while since I have used mine, but when I did I used to get it consistently yellow and then weaken from there until blue streaks could be seen in the flame front . I would then also check with a CO meter, and aim for about 4.5 to 5.5% CO - probably at the richer end of that spectrum . I think Malcolm's suggestion of working in the opposite direction will probably work just as well

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abowie
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#6 Re: Gunson Colortune

Post by abowie » Wed Dec 19, 2018 12:22 am

I haven't really found mine terribly useful. Spend a bit more and get a CO meter.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
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PeterCrespin
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#7 Re: Gunson Colortune

Post by PeterCrespin » Wed Dec 19, 2018 1:49 am

abowie wrote:
Wed Dec 19, 2018 12:22 am
I haven't really found mine terribly useful. Spend a bit more and get a CO meter.
Generally good advice but you can't separate the carbs by exhaust pipe.

I bought five colortunes to add to the one I already had, because I had six carbs to tune. A Weber DCOE is two carbs sharing a common float bowl. It was interesting to see the differences between the current items and how they were in the old days.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 97 XJ6L

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abowie
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#8 Re: Gunson Colortune

Post by abowie » Wed Dec 19, 2018 6:07 am

PeterCrespin wrote:
Wed Dec 19, 2018 1:49 am
abowie wrote:
Wed Dec 19, 2018 12:22 am
I haven't really found mine terribly useful. Spend a bit more and get a CO meter.
Generally good advice but you can't separate the carbs by exhaust pipe.

I bought five colortunes to add to the one I already had, because I had six carbs to tune. A Weber DCOE is two carbs sharing a common float bowl. It was interesting to see the differences between the current items and how they were in the old days.
Not too hard to do. Essentially I set all the jets at the same level below the bridge and then make "front 3" and "rear 3" adjustments, keeping track where the middle carb goes. When I have the correct CO in both L and R pipes I then remeasure the jet heights and average them out and then recheck and adjust if necessary. You really need to start from a level playing field but it's pretty easy once you get the hang of it.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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#9 Re: Gunson Colortune

Post by norman m. macleod » Wed Dec 19, 2018 12:05 pm

Hi all.....
Like Peter, I have used these devices since their introduction in the Sixties, on everything from single-cylinder motorcycles to the Jaguar XK engine, and just about everything in between. On the E-Type I use three. And, like Christopher, I end up moving from a blue flame indication to a partly blue & yellow flame, that takes about 1/3 of a turn richer on the mixture screws..........
May I also take this opportunity of wishing all of the Forum members all the best for a safe and enjoyable Christmas, and for their endeavours in the coming New Year........
Kind regards,
Norman.
1967 S1 2+2

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Woolfi
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#10 Re: Gunson Colortune

Post by Woolfi » Wed Dec 19, 2018 5:13 pm

"Again, I agree with Malcolm : XKs run best at a stoichiometric ratio of about 12.5 : 1 rather than the ideal ( weaker) 14 or so."
? ? ? 12,5 AFR at which level of power ? At iddle, lower part throttle or higher part throttle ?
If you adjust the mixture for all 6 cylinders at IDLE to a AFR of 14,7 (Lambda 1) , you don't know which AFR the motor has at low part throttle or half throttle or high part throttle or full trottle. The mixture depends on the shape of the two or three carb needles. If the car has another airfilter or another exhaust system, the mixture can be weaker, allthough the mixture was adjusted to 12,5 AFR at idde.
People often missunderstand, that the AFR at iddle is only similar to the AFR at part throttle, if the shape of the needle and the surroudning of the motor is like new from production.
If the airfilter or the exhaust system have less restriction than the oroginal, the mixture becommes weaker at part or full throttle. If the mixture of such a car is adjusted to the correct AFR at idle, it is automatically too weak at part throttle. Them the car runns bad.
If you adjust the micture at idle to AFR 14 (little bit fat) at iddle, it can be weaker than AFR 16 at part throttle.
I have read in a book (1965) from a university , that for part throttle the best mixture is roundabout Lambda 1,1 = AFR 16,2. This is good for a low gas consumption.
My own EV12 is running PERFECT at part throttle with a AFR of 15.5 - 17. Absolute no problems with missfiring. At WOT the mixture must go to AFR 14 - 12.5 , for inner cooling of the cylinder. Also at idle a mixture of 12,5 to 14 is best for a good idle. If the mixture is weaker than Lamda 0,95 misfiring starts to occure.
A V12 HE Motor is running well at part throttle up to AFR 18.
Small carb airplanes run at part throttle with a lean mixture. If someone wants to understand the relation of mixture and motor running, there are some articles n the internet about the adjusting of the mixture at flying.
If a motor is running at part throttle with a fat mixture, the back of the car is becomming dirty brown, the gas consumptio is higher and the exhaust gases have a bad smell.
To check how the mixture is at part throttle when driving, you need a lambda measuring system with a wide-band "lambda-feeler" and a gauge in front of the driver.
Regards Wolfgang Gatza
Last edited by Woolfi on Wed Dec 19, 2018 5:36 pm, edited 1 time in total.

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malcolm
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#11 Re: Gunson Colortune

Post by malcolm » Wed Dec 19, 2018 5:34 pm

I'm sure that's perfectly correct Woolfi, but to keep it simple (for simple people like me) I just know that if you get it to where it burns blue at tickover, then enrich 1/4, it burns yellow under throttle and seems to run very well at all throttle openings, while giving me average 23mpg on mixed running.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#12 Re: Gunson Colortune

Post by christopher storey » Wed Dec 19, 2018 6:44 pm

Sometimes I despair. SU directions for setting have always to my knowledge been to set the mixture at idle. This goes back to my own Morris 8 series 1 ( 1934 ) and to the manual I still have somewhere for my late Father's SS 2.5 litre of 1937. All settings at anything other than idle were achieved by the needle shapes coupled with the springs, which were the subject of exhaustive testing ( no pun intended :bigrin: ) by SU in conjuction with the engine manufacturers . One of the beauties of constant depression carburetters is that there is no need for complicated emulsion tubes , secondary venturis , idle and main jets, pump jets or the testing which is involved if any of these are altered. This is why the SU is IMHO the most elegant mixture control device ever invented, and why the cars which were fitted with them almost always were ( provided the manufacturer's specification was not interfered with ) significantly more economical than similar engines with other devices.

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#13 Re: Gunson Colortune

Post by PeterCrespin » Wed Dec 19, 2018 10:34 pm

“Not too hard to do. Essentially I set all the jets at the same level below the bridge and then make "front 3" and "rear 3" adjustments, keeping track where the middle carb goes. When I have the correct CO in both L and R pipes I then remeasure the jet heights and average them out and then recheck and adjust if necessary... it's pretty easy once you get the hang of it.

Agreed. I rarely use the Colortunes Unless I’m working on something totally non standard.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 97 XJ6L

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#14 Re: Gunson Colortune

Post by abowie » Thu Dec 20, 2018 12:04 am

christopher storey wrote:
Wed Dec 19, 2018 6:44 pm
This is why the SU is IMHO the most elegant mixture control device ever invented
Precisely. All you need do is set the idle correctly and everything else has already been done for you. Such clever analogue technology.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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Series1 Stu
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#15 Re: Gunson Colortune

Post by Series1 Stu » Thu Dec 20, 2018 6:10 pm

The SU carburettor is, as Christopher (sort of) says, arguably the most elegant carburettor ever. That is, elegant in its simplicity (see my tag line to get my take on that).

The most elegant mixture control device? Perhaps not, although it will continue to function long after that dreaded magnetic pulse has rendered all microprocessors ineffective.

Also, +1 for Colourtune. Simple and effective, just like the SU carburettor but remember to take it out before test driving the car.

Regards
Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
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