electronic ignition means may be movable from a position in advance or a retard position relative to top dead centre tdc which is shown in fig3 a suitably an advance position may be up to 35 u00b0 in advance of tdc and a retard position may be up to 5 u00b0 in retard of tdc these values are representative of a range at which the spark plug may fire with consequential fuel combustion in one form of achieving this objective the electronic ignition means may be movable to achieve an advance or retard position as described above this may promote easier starting between idling and better performance of the engine thus in certain circumstances it may be beneficial to move the electronic ignition means from a retard setting to an advance setting thus the electronic ignition means may be initially in a retard setting when the engine is started and moved substantially to an advance position to develop more power in this regard the engine would be easier to start in a retard position because of lower compression resistance and quicker combustion this embodiment is shown in fig5 6 wherein there is shown piston housing 11a having cooling fins 13a in a side wall thereof as well as outlet port 15a the inlet port is hidden from view in front wall 16a of piston housing 11a there are provided cooling fins 20a spark plug 21 is mountable.