How to find which Cylinder Misses.—Endeavour first to ascertain which cylinder is the culprit. One method of doing this is to place your hand on each exhaust pipe while the engine is running. You will then get a bad burn from every one except that belonging to the faulty cylinder. A more convenient way—if electric ignition is fitted—is to stop the working of three out of four of the induction coils, changing about until you find the one that is at fault. It may be, however, that your engine has only one cylinder, or that all the cylinders miss occasionally.
Let us take the various possible causes of the difficulty.
Cause 1.—Be sure that the governing gear is working properly, and that the governor does not cut out one cylinder when it ought not.
Cause 2.—The induction valve may be worn, and opens too much.
Cause 3.—Exhaust valve lifters worn and do not lift enough.
Cause 4 (rare).—They have expanded through being overheated, and open too much.
Cause 5.—A spring displaced.
Cause 6.—The exhaust or induction valve springs are not strong enough to close quickly, and an exhaust valve may sometimes open on the suction stroke.
Cause 7 (rare).—The mushroom-shaped fitting called the diffuser, which is part of the small disc screwed into the top of the carburator, may be too near or too far from the jet of petrol.
Cause 8.—Or the size of the nipple through which the jet is sucked is too large or too small. It is very seldom that this should be touched, and its adjustment must be made with extreme delicacy, by the aid of a watchmaker's brooch-needle. It is always best to make any experiments on a spare nipple, and not to touch the one that is in use, so that if unsuccessful you may put back the old one, otherwise the last state of your carburation may be considerably worse than the first.
Cause 9 (rare). Freezing of the carburator. Trouble will sometimes arise through the carburator freezing, even in warm weather. The remedy is to fit a pipe to convey to it air heated by the exhaust or the burners.
