If the Engine Stops. See if tank is empty. See if petrol tap is turned on. Examine sparking plug. Examine contact breaker. Examine carburetter jet, see if clear. Vent hole in petrol tank cap may be blocked.

Engine Stops or Misfires Badly. The most probably cause is the sparking plug (see Sparking Plugs, below). It should be clean and dry externally, with the cable firmly fixed to plug and coil. If cable is burned through this would cause short circuit ; the remedy is to bind the exposed wires with insulating tape until a new wire can be fitted. Should carburetter cable touch sparking plug this may cause the engine to stop. If the plug is oily inside, clean with petrol, see that there is no dirt between the points of the plug. See that the contact breaker is working properly. Look over the electric wires and see if any connections are loose or any wire chafed through.

Engine Stops, fires a few times, and stops again. By far the most probably cause is partial failure of the petrol supply. If a restart cannot be made by tickling the carburetter float, examine the carburetter and see that the small gauze on the petrol tap is clear ; at the same time see that the petrol runs freely when the petrol pipe is disconnected from the carburetter. A small obstruction may be in the tap or pipe itself. Examine the jet, also the base of the jet, and make sure that it is quite clear. The vent hole in the petrol tank cap may be blocked. Examine the inlet pipe and the cylinder face. Possibly the inlet pipe will want screwing up or a new packing inserting between the cylinder and the inlet pipe faces. The carburetter should be well pushed up on to the inlet pipe, and the clip should be fastened till it holds the carburetter rigidly.

Four Stroking. This is generally caused by either over-oiling or defective carburation. If it is over oiling reduce the supply. For very slow riding the smallest supply of oil is sufficient. Over oiling is generally accompanied by a considerable quantity of smoke from the silencers, and also causes oil leakage at the joint of the exhaust pipe nuts and the cylinder. Where carburation is at fault, look for the following troubles : Flooding, jet too large. Other possible causes may be defective sparking plug, points too near together, or plug of unsuitable design, incorrect adjustment of the contact breaker, or timed too late. A booklet on the carburetter can be obtained from the Makers.

Timing. It is not usually necessary to remove the cam or the contact breaker, but if this has been done and it becomes necessary to retime it, proceed as follows : Fit the cam on the contact breaker spindle so that it can be turned on the shaft. Check the opening of the contact points ; these should be set to .018" to .020". Set piston exactly on top dead centre. Make a mark on the flywheel corresponding to some fixed point on the engine. Turn flywheel backward till this mark is 2 3/4" from the above fixed point. The contact breaker cam should then be set, so that the points are just breaking with the ignition lever in fully advanced position. It is possible to check this accurately by replacing contact breaker cover and connecting up the wire. The ignition should then be switched on, and the engine turned forward. The ammeter will show a discharge until the moment the points separate. The ammeter needle should return to zero when the marks on the flywheel are in the above described position.

The same setting as given above should be used for machines fitted with magneto ignition.