Sparking plug
Page 68
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For those concerned with obtaining the best from petrol engines without expensive tuning equipment, a new type of sparking plug with a transparent glass top. which enables one to look into engine cylinders and study the combustion flame while it is actually burning, has been introduced by Gunson's Colorplugs Ltd It is called Colortune 2 and makes correct carburettor tuning a comparatively simple. visual job.
The Colortune 2 can be used on all four-stroke and twostroke engines fitted with carburettors having fixed or variableaperture jets, and also on engines
fitted with petrol injection systems. It will operate at up to 5,000 rpm and can be used on short road tests at up to 50 mph 180 km/W. It is available with 14mm OT I Brnm diameter thread mountings which screw up to a maximum of 19m liin.) into the cylinder head. The thread length can be reduced to match that of normal sparking plugs by means of a spacer ring and copper-covered asbestos gaskets. The unit is packaged together with a simple maintenance kit and includes a booklet giving detailed instructions for carburettors made by Zenith, Solex, Stromberg, Weber. SU, and Amal. Individual guides are available for other makes.
A rich mixture burns orange: weak burns whitish blue. Both are wrong for any petrol engine. Between these two extremes easily recognizable colour grade
tions occur. An intense light blue similar to a Bunsen flame indicates an air/fuel mixture of 12:1: this mixture gives maximum economy and power in performance for engines with variable jet carburettors. Intense whitish blue combustion indicates a mixture of 15:1, which is correct for engines with fixed jet carburettors. Most petrol injection systems also lie within this range of ratios.
Made by: Gunson's Colorplugs Ltd., 66 Royal Mint Street, London. El.
Price: £4 lit 6d.