It's the first show of the season, and the antique engines have been carefully polished and cleaned. A small crowd gathers as the first exhibitor prepares to start the morning off. After carefully priming the engine, he fits the crank into place and starts to roll over the flywheels. The flywheels gain momentum, and the engine pops to life. But that first pop is as lively as things get. The engine slows and then stops completely. The crowd moves on, with some remarking on how great an idea the electric starter was. The lone exhibitor is left scratching his head and prepares himself to devote the rest of the day to figuring out what is wrong.
Diagnosing and fixing an engine can be very frustrating, especially for newcomers to the hobby. Many times the manual, if one can be found at all, is very sketchy about diagnosing engine ailments. Although there are an infinite amount of failures which can cause an engine to run rough or not at all, look first to the ignition system. More often than not, the cause of the trouble is a weak spark. Here are some causes of weak sparks and what can be done about them.
Carbon and soot produced by burning fuel without enough air is the enemy of ignitors. If the engine is set too richly or primed too much, the ignitor contacts may become coated with carbon, and the spark will lose its strength. To be efficient, the metal contacts must be clean, whether these be the metal terminals on a spark plug or the points on an ignitor. Figure 1 shows the critical areas that must be clean and dry in order for a hot spark to form. Remove the ignitor or spark plug and use sandpaper or some other abrasive and thoroughly remove any carbon buildup from these spots. Then ground the ignitor or plug, roll the engine over, and observe the spark produced. A hot spark, preferably blue in color, should be visible. Be sure to let the engine go through several revolutions. One good spark is not enough; there must be a good, hot spark each and every time.
With the exception of spark plugs, ignition systems generally have several springs attached to them. These springs act to hold the ignitor contacts firmly together. If the ignitor contacts are not firmly together, the circuit will be broken and no spark will be produced. Since the ignitors are often located near the water hopper, springs can be heated to high temperatures, and their tension is weakened. Be sure to check all of the springs while the ignitor is apart. Work the mechanism several times to ensure that the contacts do indeed close every time. Working the mechanism by hand gives a better picture of what is going on inside the engine.
Engine designers of yesteryear did not have access to the sophisticated gaskets of today, and as a result, water finds its way into everything. A hot day followed by a cool night can cause condensation on metal parts. Water alone makes combustion more difficult, and when combined with traces of carbon, an electrical circuit can form anywhere but where it is needed for a spark. A good precautionary measure is to cover magnetos, ignitors, and plugs with plastic. This causes dew and rain water to form on the plastic instead of the part. Also, be sure the cylinder well is drained. A stopped up drain hole can cause formation of a pool of water, which is then splashed into the cylinder by the crankshaft.
A well-tuned ignition system can make starting a lot easier. Hot sparks are an essential part of a reliable engine, and many engine problems can be traced to flaws in the ignition system. Properly checking and testing ignitors and spark plugs first will greatly reduce the frustration factor, and will get the show up and running quickly. Have a happy show season and keep those sparks hot!