SWEET ACCELERATION

Evening Post, Volume CIX, Issue 51, 1 March 1930, Page 27

SWEET ACCELERATION

Small high-efficiency engines are very liable, to knock if the driver attempts to force their speed up from a slow pace to top goar without using his spark lever. The reason for this becomes obvious when one considers tho conditions ruling in the inlet manifold and cylinders (luring acceleration. As the engine is running at low speed on a nearly closed throttle, the cylinders are only partially filled, and as the gas is mixed! by the slow-running jot, it is richer and slower burning than the normal supply. When the driver suddenly steps hard on tho accelerator the restriction is taken off tho incoming gas and the cylinders receive their full quota of fuel. Unfortunately the mixture is by no means homogeneous, and as the air commences 'to pour into tbe cylinders before the comparatively heavy petrol vapour has a* chance to got under way, tho mixture is weakened below normal, and knocking is set up. If, however, the driver retards the spark just before lie. pushes ihe accelerator .pedal, down, by providing a late'"Spark,'he counteracts the r;i.pid-burning tendencies of the weakened fuel, and thus knocking is avoid-

cd. -Immediately after tho accelerator has been pressed down, the ■ driver should commence advancing the spark, moving the lever gradually to tho advance position to suit the rising speed of tho engine. Tho secret, of success iii. this connection is to mako the movement of the spark lever synchronise perfectly with tho demands of the engine, and if this control is expertly hatidlod. the- acceleration will be sweet: and astonishingly rapid.