The careful driver will get used to the particular sounds made by his machine when running, and listen at all times for any difference. Any such difference means that something has altered its behaviour, and the sooner this is detected, and dealt with, the better. The above does not mean that his driving time is to be taken up listening for sounds, but simply that he trains himself to quickly note any difference. Another thing that a careful driver does is that, in the event of say an engine stoppage, he proceeds to make one adjustment or altera-tion at a time, and notes the result, finally he will find the cause of the trouble and the remedy, and is therefore richer in experience and knowledge. The careless driver will alter many things at once, and quite likely get things going again, but is not then at all sure as to what happened, and is not a bit wiser for future use. Engine will not start. The cause of this must rest in one or more of three places, i.e., (1) the engine; (2) the carburetter; (3) the sparking plug. Taking these in turn, and dealing with the engine first, make certain that the compression is good, and that the engine rotates freely. If it is a four-stroke, rotate it smartly with the carburetter levers set open, and test the compression by standing on the starter lever (if a kick starter); good compression should be easily felt. If the compression is extremely bad, it will account for the starting difficulty, and the cause of the bad compression must be found. It will probably be either a sticking valve, or a broken valve or valve spring, but might be a cracked piston or cylinder, failure of the piston rings, or valves badly, require grinding in. As a guide in some degree it should be ascertained or remembered as to how the engine behaved when last running, if perfectly, then while any of the above troubles are possible, yet they are not likely. If the engine is very stiff to rotate, suspect want of oil, or too stiff an oil. Ascertain whether rotating the engine more smartly has any better effect. In extreme cases the valve timing might have to be checked over to see whether the valve gear is working correctly ; this, however, is a very unlikely fault nowadays. Turning next to the carburetter, see that the petrol is really turned on, also that the tank is not empty. If it is a type that can be flooded, try it, and so make sure that petrol is really reaching it. Next make sure that the jet is clear and the float free and working properly.

Be certain that the petrol is not very old and stale, especially the contents of the carburetter. Make sure that the levers, when moved, do work the attached parts of the carburetter, the connecting wires might be broken. Make certain that no parts of the carburetter have become loose, or come away, due to vibration. Try the effect of altering the mixture when rotating the engine. Inject a small charge of petrol into the engine, through a compression tap, or sparking plug hole, and try the effect of engine rotation, if it does not even fire then, it would appear that the fault is more probably due to the plug or its accessories. If, however, it does fire once or more, it points to a fault in the carburetter; check the float level. Turning to the sparking plug, first try the effect of altering the position of the spark advance lever. Many machines are quite fussy about having this in one particular place, and this place must be found by trial. If this does not prove successful, see that the plug points are clean and not more than 1/32in. apart. Change the plug for a known good one. If still not successful, examine the high tension wire from magneto to sparking plug, see that it is in good condition, and really is attached at both ends. Take the good plug out, | keep it attached to the high tension wire, place it on the engine cylinder top, rotate the engine, and watch for the spark at the plug points; if weak or absent, then proceed to the make and break contacts on the magneto. Take the cover off, on the contact end, and get someone to slowly rotate the engine while you watch the make and break lever to see whether it is not stuck up. If it works really well, then it probably may be that the platinum points are dirty; clean very carefully with either a very fine file, or a piece of folded fine glass or emery paper. See also that it opens just the right amount, most magnetos require about a bare 1/32 in. opening between the points when fully opened apart. When satisfied that all is correct there, then try again to start the engine. If still not successful, note whether the plug sparks or not, if not then examine the carbon pencil that passes the charge from the magneto to the high tension wire, see that it can press easily on to the collecting ring on the magneto, and that it is clean. If still there is no spark, hold the end of the high tension wire with the fingers of one hand, and touch the engine with the thumb of that hand, while someone else rotates the engine, a shock should be felt, it can do no harm, the shock will be through the hand only and not through the body. If no shock, then after making sure that the magneto really does rotate at the proper speed, and that the contact breaker is working properly, also the carbon contact pencil properly in contact with the collecting ring and that no dirt or film of oil is present anywhere in the circuit, and that the high tension cable is perfect, then the magneto is itself at fault, and this is not a roadside repair at all. Present-day magnetos are, however, remarkably reliable, and the possibility of such a fault developing is very remote. If there is a good spark even at the plug, and all else appears correct, then check to see that the spark does occur at the right instant with relation to the position of the engine piston, as the spark timing gear might have loosened and slipped. In the event of an engine refusing to start, and it appearing a bad case, the bothered driver should keep firmly in mind that provided the engine is in good order, is rotated at the proper speed, has a proper supply of petrol mixture offered to it, with a good spark at the right time, then it must start, no petrol engine ever yet failed to start under such circumstances, or ever will fail to start.