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that with petrol as fuel the compression was still too high. No type of spark plug could withstand the abnormally vehement explosions.

Ricardo's well known experiments on various fuels for aviation engines formed an inducement to change the fuel for one with a high "toluene value". A mixture of benzol and petrol in proportion of 60 : 40, using benzol with a high toluene percentage (physical properties of the benzol used):

Sp.W. = 0.86
Freezing point: from -20° C to -35°C.
Distillation range: from 80° - 85° C. to 
110° - 120° C. :

95%, about 60% beneath 100°C., gave very good results and was adopted as a standard fuel. 

No compression troubles occurred since then. 

The ignition in these motors is by means of two Bosch Z.H.6 - '14 magnetos which are a special lightened type of aviation magneto. These proved inadequate. In the Dutch Air Service the normal Bosch Z.H. 6 magneto is mounted instead.

Apart from this it was found that the magneto mounting was badly designed so that another type of mount was substituted.

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