Engine Stops Firing Suddenly

Generally this will be due to an electrical reason. The high tension wire may be jolted off at one end or the other. The sparking plug may have suddenly broken down, so that no spark occurs at the points. Indeed if the stoppage was really sudden, without any other sounds or signs, then it is almost certain to be due to an electrical fault. A broken valve, or badly broken spring may, however, cause a sudden stoppage, but will make a difference in the usual engine sounds, so that it is easily recognised, indeed any engine fault ought to be so recognised.

Engine Stops Firing Gradually

This points rather to a petrol or carburetter trouble, and it may or may not occur with misfiring also. See whether the petrol supply is alright, also carburetter clear, see also as quickly as possible after the stoppage whether the float chamber in the carburetter was full, if so, and the jet was clear, then suspect the sparking plug. Some of these can perform remarkably sometimes, and a case has been known where a plug allowed the machine to be run for five miles only, then while the carburetter was being cleaned out, the plug cooled down, and worked well for another five miles, and so on, until the fault was discovered. Another possible fault is an air lock in the petrol tank, clearly when petrol is being drawn out of a closed tank there comes a time when no more will flow out, a fine clear inlet for air to replace the petrol drawn out must always be provided.

Engine Sometimes Difficult To Start

This is due to either of several causes. Make certain first that the engine is being rotated fast enough, this, however, generally is done. See that the sparking plug points are not too far apart, adjust to say 1/32in. Change the sparking plug for a new, or for a known relia-able one. It is absolutely no guide that because a sparking plug will fire reliably at slow or high speeds, that it will properly start the engine at the lower starting speed. If still the engine will not start, and it is certain that the engine itself is in good order, no valve sticking for instance, also that the spark and plug are correct, then it must be the petrol supply or carburetter. Ascertain whether the petrol level in the float chamber is correct, try the effect of raising the level. If the weather be very cold, try the effect of a cloth (soaked in hot water) wrapped round the carburetter. Make sure that the petrol is turned on, and that the jet is not blocked. See that the carburetter is not flooding, i.e., overflowing, so giving too rich a mixture. Try the effect of altering the position of the spark advance lever, also the carburetter levers.

Engine Looses Power

Probably due to the loss of compression, but may be due to bad petrol, or partial stoppage in petrol supply, which might be due to a block in the pipe, or perhaps an air lock in the petrol tank. If the engine is much hotter than usual, stop and allow it to cool down, make sure that the lubricating system is working properly, and that the machine brakes are not adjusted too tightly, and therefore on, the whole time. The valve timing may have gone wrong, but this is a rare fault. See that all bearings are cool and correctly adjusted. See that the valves open fully.

Engine Will Not Run Fast

Probably the spark advance is retarded, or the petrol supply is insufficient. The valves may not open sufficiently, or there may be a partial stoppage in the silencer. It may also well be that the work being done is too much for the engine. It is somewhat rare to find an engine that will run slowly and well, and yet not fast, the reverse is much more common.

Engine Will Not Run Slowly

By slowly it is understood, slowly and regularly. It may be due to rather poor compression, or a defective spark, and this defective spark may be either intermittent or poor in quality. Again, it is necessary for very slow regular running that the volume of petrol mixture in the cylinder is quite uniform in strength or quality. This cannot be the case if an air leak is present. See that the valve chamber caps, also the seat of the sparking plug, do not leak; lay a trace of oil around the seats, and watch for bubbles while the engine is firing. Examine also the valve guides; these may be badly worn and allow air to leak through in varying amounts on different strokes. If badly worn, get them bushed, or use one of the valve stem packings on the market. Properly adjusted, even a single cylinder four stroke engine will fire regularly at a very slow speed, and then is generally a very easy starter.

Engine Misfires

Most probably a defective plug, but may be a fault in the carburetter. If it persists, it is more likely to be a spark trouble, as a carburetter trouble is likely to clear itself, or get worse.

Engine pre-lgnites. Generally due to engine being too hot, or requiring decarbonising. It may possibly be defects in the plug points, but this is rare. Change the plug to a known reliable one.

Silencer Explosions. Due to the engine not firing on one stroke, and passing the unfired charge into the silencer where it is fired by the next fired charge. If a multi-cylinder engine, it may be due, of course, to either of the cylinders misfiring.

Engine Knocks

Generally due to the spark being too advanced either for the work being done, or for the speed ; retard the spark. It may be pre-ignition, but is not likely nowadays. It can be due to the cylinder or piston head or both being covered with burnt oil; examine and clean off. See that the engine lubrication is all in order.

High Petrol Consumption

Due to either bad driving, use of too big a carburetter jet, a leak somewhere, or piston rings or valves leak. Now as to the bad driving the engine should not be kept on a low gear any longer than absolutely necessary, and always the mixture should be given as much air as it will take. The spark should always be as far advanced as the engine will allow without " knocking." The size of carburetter jet should be experimented with, and the smallest one used that will give satisfaction. Look well for any petrol leaks, even a slow drip uses up petrol considerably in a day's run, it should be put right at once. Leaking piston rings or valves will reveal themselves by poor compression; test for this, and put it right. If the engine has a detachable cvlinder head see that the joint between it and the cylinder is good ; if not, remake it. See that the piston rings are in good condition, and that the joints do not face one another. There may be a leak through the sparking plug, and it will be indicated by a slight discharge of oil through it from the cylinder, i.e., a thin brown film will be seen; a new plug is generally required.