Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Tuning with a Colour Tune

Any comments on the use of a colour tune when setting the mixture on twin su's. Are they effective?.
Kim R.
K Rutherford

I have used one a few times, they are very good for getting the two carbs balanced but you have to remember that on the B cylinders 1 & 4 run a little weak and 2 & 3 run a little rich, you have to take that into account when setting the mixture.

The colourtune takes a little practice and you have to have excellent colour vision, If you are colour blind forget it, you prbably will not be able to use it accurately.
The Wiz

Kim. Some of us whom have passed a number of tests for color blindness still have problems using this tool. Mayhap it is the blended fuels that we have to use, but, I could never get the correct "Bunsen blue" color depicted in the charts. I gave mine away years ago. To me, it was a waste of money. Les
Les Bengtson

Just not having good luck getting the mixture right, and can't seem to get them both equal.
Kim R.
K Rutherford

I guess I do have a teeny advantage, I'm a printer and I work with colour for a living, your eyes do tend to become accomplished at distinguishing between very subtle shade differences when you spend all day looking at colours.

As I said, the colourtune does take practice, you may have to mess with it several times before you get the hang of it. Don't give up on it yet, try it a couple more times at least.
The Wiz

I've been using one for years and find it helps dial in the mixture. I go from lean to rich and back again to see the variable between the 2 points and set it in between the 2 points. I then go for a cruise and check the plug color. It's not an exact science but it did help me choose needles across the rpm range on a modified engine.

I also use a CO2 sniffer up the tailpipe to witness under load conditions.
Mike MaGee

Kay. An inexpensive set of dial calipers are available, from several sources, for under $25US. Peter Burgess recommends an initial setting of the jet at .060" below the bridge of the carb body. Removing the dashpot cover, spring and piston allows you to set this very easily. Properly dialed in, I find that the jet being about .055" low works fine. If all else is correct--i.e. the cylinders are in good condition, the valves are in good condition and the cam is not worn, setting the jet .055" below the bridge and driving the car works just fine and is far more exact than the "tune by ear" methods and, in my experience, better than investing in a ColorTune. The ColorTune did now work very well and can only accomplish a single mission. The dial calipers work better and can be used for quite a number of different measurements.

Les Bengtson

I've often thought about getting one of those things. Bought one of those flow meters years ago - it has been stuffed in a drawer for at least 20 years. Never could get it to work to my satisfaction. The sensitivity just wasn't there.
I don't have any of those fancy analyzers, so I tune my SU's primarily by ear and observation. Starting with near balanced compression, proper valve clearance, correct ignition tuning, good plugs, clean carbs, linkage clearances checked, free moving pistons, topped-up damper oil, I balance intake and adjust idle as described in the Bentley manual. I don't use a flow meter, however. I prefer, instead, a 2 ft length of 3/8" rubber hose with one end placed just inside the lower lip of the carburator's throat and the other end plugged into my ear. Mixture adjustments are also performed as described in Bentley's manual. I fine tune my mixture adjustments by driving performance and pulling the plugs and examining them after some short city driving and some distant high speed freeway driving. Most times, I only need to adjust a flat or so. I generally get mid 20's city and low to mid 30's highway.
Steve Buchina

I also have and use the color tune. I also have difficulty in seeing the actual color. Not the best thing to look at with bifocals.

I find it a good tool to get the two close. Les. I am going to try your recommendations also.
Bruce Cunha

Into how many cylinders must one install the colortune to get an "accurate" measurement? And in what sequence?
Gary Kinslow '69B roadster Pale Primrose

Into 1 cylinder for each of the carbs. I generally do 1 & 4. Not an exact tool but it does help dial in your carbs.
Mike MaGee

Always nice to see conflicting opinions.
I've used my Colortune several times on the twin HIF's and like it VERY MUCH, but I only use it as icing on the cake, after adjusting the valves and ignition and balancing the carbs.

Because of the balancing pipe on the manifold I test cyl 1 and 4 two or three times for the best results.
Because of my colorblindness (...) for extra contrast I use it in a darkened garage, with a hose that ends outside on the exhaust.

As said, it is important to balance the airflow in the carburettors first. Start with the butterflies and let them open/close exactly the same, after that check the airflow with a dail.

When you don't have a dail, here are two amateur alternatives, (somehow listening with a hose doesn't work for me):

Pour a little petrol in a transparant hose, connect the ends of the hose to the pipes on the carburettor where normally the enginebreather pipes are fitted. Let the hose hang down in a loop so that you have a left and a right fluidlevel beside each other. Fix the bent hose to a plank and mark the fluid levels. Start engine. If the airflow is the same in both carbs, the fluidlevels stay on their marks. If one carbs "sucks harder" the corresponding level will rise. The aim of course is to reach fluidlevels "on the marks" on various RPM's

I like this one very much. Unscrew and remove the dashpot dampers. Replace the dampers with a thin wooden stick, so that it sticks out of the dashpot. Fix to the sticks two stiff wires and let the wires point to each other horizontally between the carbs, cut the wires so that they just dont touch. Bend the wires so that they are exactly on the same level. Start engine and strive for more or less same level wires on various RPM's!
Willem van der Veer

I like the colourtune and use it is cyls 1 and 4 but use this also in conjunction with a flow meter (like your ideas Willem and will try them) Obtain balanced flow and at the same time working from a rich yellow flame aim to just eliminate this. If you work this way you will obviate the need for comparing blue colours.

Now I see where Les is coming from and provided everything is unworn including needles and jets this could well work but it does not make allowances for individual motors. Use it by all means as a starting point but I'd do a final check with the colour tune.
Iain MacKintosh

As far as using a Colortune with HIF4's, I find it a waste of time. Could never get the bunsen blue color, only yellow-orange lean color no matter where the jet screws were set. Found that the best method of mixture setting was to use the technique shown on the label on the bonnet lock platform or owner's handbook: set to highest idle speed then lean out until idle speed begins to drop. Need a digital tachometer to do this easily but it works. Also found that the car runs best with the jets set slightly richer (1/8 turn) from the point of idle speed drop. Of course, the rest of the tune-up items have to be just right and the carbs have to be in good condition for this to work.
willie L.

Willie, Yellow / Orange is rich not lean, seems that you might have got the thing confused. Lean is the other way going towards a whitish flame. If you keep getting orange spots that is an indication of oil burning.
Iain MacKintosh

Have the car running well now. Installed a new set of plugs, took the long tube off the Colour Tune and used it in the semi dark, nice idle, and all is well. 1
bad plug was'nt helping matters.
Kim Rutherford.
K Rutherford

I have used the Colortune successfully on my A and B for some time now. I install it on 1 and 4 cylinders and adjust the corresponding carb. With the engine at about 1000 RPMs set the carb mixture to a yellow (rich) flame then adjust until it just turns blue, push the jet up to make sure it is against the adjusting nut, rev the engine a couple of times to be sure it stays in the blue range then switch cylinders and do the same on the other carb. Repeat the whole cycle one time to make sure its stable.

Bill Boorse

I agree with Les. A good set of calipers,a Unisyn and a timing light, are all I need to get the beast purring well.With new plugs,wires,rotor,cap and air filters, the exercise is easy. You simply can not tune around old "stuff" Alyn

Another vote for the colourtune. Very helpfull on the C aswell, with 3 cylinders per carb and differing inlet lengths.
I found that if you can't get the colour right, you very likely have a problem with your engine.
Rufus Pool

This thread was discussed between 24/09/2005 and 29/09/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.