Tuning Triple Carburetors

Reprinted from Midlands Centre Magazine, November 1979


Before attempting to tune your trip carb machine, you should make sure you have the basic tool kit which comprises:

  • one screwdriver not previously used as a chisel

  • pliers

  • molewrench (vise-grip)

  • one pair Vernier Calipers

  • one length of plastic pipe

  • 24" Stillsons

  • 2 lb. lump hammer

  • pencil and paper

  • stout tin box with lid

  • candles

  • cigarettes and matches

  • first aid kit

  • Keith Boyers' telephone number (or Mike Daniel's)

Having assembled all these, you are now ready to start. Open the bonnet (most Big Healey owners, with one notable exception, can reach this stage without expert assistance), and locate the carburettors. If there are less than three, do not read on, or else ring the police to report the theft.


Using the calipers, pencil and paper spend the next hour carefully recording the exact position of all the slow-running adjusters, throttle stops and volume controls that you can find. Put the paper, pencil, calipers and a candle into the tin box and remove the whole thing to a place of safety.


Remove the air cleaners; this will expose the barrel and piston of the S.U. If no piston is apparent there are three possible explanations:

  1. Some clever b****** has fitted triple twin-choke 45 DCOE Webers. Further advice is futile; shut the bonnet at once and concentrate on fitting a 25 gallon petrol tank.

  2. You are running on Triple Solex and probably qualify for the Guinness Book of Records.

  3. You have a serious problem; ring at once for expert assistance.

Assuming you have reached this stage, disconnect the throttle linkages so that each carburettor will function independently of its fellow. Slacken off all the slow-running adjusters and then tighten each by one and a half turns. Now is the time to roughly tune each carburettor in turn.


Start the engine. This may provoke hysterical laughter from the average Big Healey owner. Why do the manuals always assume that the thing will actually run in that condition? Anyway, let us assume that it does. Starting with a carburettor of your choice, adjust the volume nut until, when the piston is lifted gently about 1/2", engine speed increases slightly and then settles down again. Of course, this hardly ever happens. Usually the engine stops completely or races away to self-destruction but, nil desperandum, you must persevere. (Authors Note: I am not 100% confident that these instructions are correct, and I can't really be bothered to look it up at the moment. Never mind, you can always consult your Haynes Automanual or ask the MG owner next door what he does!)


Now we come to the real mystique: balancing three carburettors. Of course, it is just the same as balancing two carburettors but three times more difficult. There are all sorts of posh ways of doing this with such things as manometers, exhaust gas analysers, etc. Personally, I prefer the time-honoured method of stuffing one end of a length of tube in your ear with the other end adjacent to the air intake of the carburettor. This enables you to balance the induction hiss of one carburettor with that of its neighbor by judicious fiddling with the slow-running adjuster. Fine, you have two carbs, but what about three?


The answer is almost magical in its simplicity. First you balance carburettors 1 and 2; then 2 and 3; then 3 and 1. By now, 1 and 2 will be out of balance so readjust them; then readjust 2 and 3; then 3 and 1. By now 1 and 2 will still be out of balance so you readjust them…….. Do you get the idea? This procedure is usually brought to a conclusion by one of three events:

  1. You fall asleep over the bonnet of the car with two feet of plastic tube protruding from your right ear. You also gain a reputation for eccentricity in your neighborhood.

  2. The engine is ticking over at 2700 r.p.m. and you are overcome by exhaust fumes and heat

  3. You sustain permanent hearing damage and are unable to detect any induction noise at all.

Let us assume that the carburettors are balanced to your satisfaction (or else you have given up the attempt). Replace the air cleaners and reassemble the throttle linkages. The time has come for the road test. The experienced coarse Healey mechanic will bid a fond farewell to his family and friends and set off with a flask of hot coffee, two warm blankets and large quantities of sandwiches.


In the unlikely event of your returning (with the car) during the hours of daylight, there remains just one final task. Find your tin box and meticulously reset the carburettors to their original condition.


Using the candle, cover the adjusters with wax to discourage further tinkering and then sit down to write out 100 times:

"I must not play with my carburettors or I will go blind."

"I must not play with my carburettors or I will go blind."

"I must not play with my carburettors... "


A final word to the average Sprite owner, who may be inspired to fit three carburettors: Sprites do not go well on three carbs; it tends to upset the weight distribution and makes them pull sharply to the left!!


Not what you were looking for? Don't forget you can check our back issues using the AHCUSA Magazine Index.

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