Ignition Problems

Spark Plug, Cap & Related

The most common cause of ignition related problems is a bad plug. They can look fine but be broken internally. They're cheap and easy to replace so start there. Other possibilities:

1. The cap's screw is bad. Caps frequently attach to the spark plug wire by screwing a center screw portion into the center of the wire. If the screw misses the wire or is barely touching it or is touching any of the surrounding braid, there will be no spark.
2. The cap is fouled with debris. Pull the cap off and see if there is any debris. Sometimes there is rubber leftover from manufacturing that gets in the way of making good contact.
3. The cap is loose. If the cap pulls off too easily then it is more likely to get fouled with black, sooty carbon which could decrease connectivity. The black substance comes from the loose plug arcing.
4. The Spark plug end is worn or loose. If you have the type of plug where the tip screws on, it may be loose.
5. Incorrectly gapped. Some motors are very sensitive to having the correct gap. A large gap requires a stronger spark.
6. Wire disconnected at the coil. These sometimes break off from vibration.
7. The wire is broken internally. It MAY run but gradually get harder to start or start cutting out.
8. The fine windings inside the coil are shorting out. This would reveal itself through a low coil resistance. According to Paul Czernecki of Planet PPG, on Simoninis at least, using the red & blue wires, 300 ohms is what new units get, and 160 ohms is so low that it won't produce a spark.
9. The Spark Plug has come partially unscrewed. Usually it blows out completely, but in rare cases, combustion chamber pressures will damage the threads, leaving the spark plug imbedded but difficult to unscrew. In that case, you must repair the threads. Don't just force it out, use this field fix.

Kill Switch

If bare or abraded (insulation worn through) kill switch wire is touching any part of the frame or return wire on its way to the kill switch, it will ground the coil just like pressing the kill button. There will be no spark. Disconnect the wire and ed. If you suspect that the fuel flow is insufficient there are two possibilities. A blockage in the fuel path or vent path. 

2008 June 17 It has been reported that an ignition based tachometer can cause problems for the kill switch. You press the kill switch but the motor doesn't shut off. So far it has only been reported on Black Devil motors but may apply to others. The problem happens when the tach pick-up wire has too many windings around the spark plug lead. It's fixed by reducing the number of windings.

Coil

These are rarely the problem, thankfully, since they're a pain to replace on some motors.Most likely one of the wires has vibrated off or it has shorted out internally. Other possible coil-related problems:

1. Broken Ground strap around the outside part of the coil on some machines.
2. Broken wire.
3. On E-start, stator coil can prevent a spark.

The coil is replace on the Black Devil 172 motor by removing the hand start mechanism with 4 nuts and removing the 2 hex bolts of the coil.

Coil (Ignition) Wire Breaking

On some models of Simonini (and probably others) there is a problem with one of the coil wires breaking. Here is the solution. Clean the electrical connections with Acetone. Crimp a connector onto 6" of Deans noodle Purple wire and run that from the coil to the other connection point. Thanks to John Black for the tip. See Simonini Ignition Page

Testing for Spark

Several things you can do to check if there's a spark:

1. Spray starter fluid (available from most auto parts stores) in the air intake and see if the motor fires. If it does, you've got spark. If it doesn't, investigate further.
2. Take the machine to a dark place (garage or similar). Remove the spark plug, put the cap back on, lay the plug so that it's threads are touching the cylinder and pull the start cord. You should see a spark as the motor turns over. You may have to cup the spark plug with your hand to see it. Pull it briskly.
3. Buy and use a spark plug tester.
4. Put your thumb across the gap and pull the cord. Pain=spark although, if you cannot visibly see a spark, there may simply be insufficient voltage from the coil.
5. The spark should have a blue tint, yellow means it may be too weak.