Home tuning made easy

Press, Volume CXIV, Issue 33442, 25 January 1974, Page 21

Home tuning made easy

It is not so long since motorists worried ahout keeping their car in tune almost solely for performance reasons. Scarcer and dearer fuel will change this attitude for good. Keeping a car in tune is now very much a matter of dollars and cents.

As garage costs rise, too, more motorists will want to tune their cars themselves, and in this regard one of the most useful aids a home

mechanic can have is a Colortune plug — a device put out by a British company, and one which has been available in New Zealand for some time. The device is basically a transparent spark-plug, which allows one to see the colour of the burning fuel-air mixture inside the cylinder as the engine is running.

The point of this is that the mixture burns with a different colour depending on the fuel-air balance, and by watching the colour as the carburettor is adjusted, the mixture can be set very accurately. The device works on any engine, although it is on car engines that it is most likely to be used. But it can also be used for motorcycles and motor-mowers, for instance.

The original Colortune plugs had one major drawback: they had to be used in a fairly dark area if the colour of the burning mixture was to be clearly visible, and one had to be standing right over the plug in order to see. This was a nuisance when using the plug on engines with the plugs on one side, and the carburettors on the other — it meant checking the plug, going to the other side of the car to alter the settings, returning to the plug, and so on.

But now the device is available in an improved

version, known as the Colortune 500, and these disadvantages have disappeared. The plug is now surrounded by a removable black plastic tube that shields it from stray light, and a small mirror on top of the tube makes it simple to watch the top of the plug from the opposite side of the engine. Most home mechanics, and some garage mechanics, tend to set carburettors too rich, which wastes fuel and increases pollution. Testing the device on two wellmaintained cars showed both were running too rich —not much, but enough to

show up significantly in consumption figures. Seen through the Colortune, a rich mixture burns orange, a lean mixture blue-white, and a correct mixture, bright bunsen blue. Setting the mixture could not be more simple. The plug can also be used to detect some engine faults: intermittent bright, white flashes mean a faulty ignition condenser, for instance. A green-tinged flame means oil burning in the cylinder as well as petrol. Two-strokes, running on a petrol-oil mixture, show a bunsen blue flame with a

purple tinge when correctly adjusted. The Colortune can also be used to time the ignition. although it is simpler to use a bulb connected across the coil terminals. But the device can be unhesitatingly recommended as an aid for home mechanics. It is worth noting that most leading car manufacturers approve of the device, and many regard it as a regular service tool. The photograph shows the device in use on an engine. The hinged mirror at the top reflects the colour at the bottom of the tube.