Polini Thor electrical wiring schematic

by Had Robinson

If there are ignition problems, the following may be useful.  If the wiring is undisturbed, it will rarely be an issue.

Polini uses the IDM ignition system.  Here is the schematic for the Thor engines.  Most pilots do not utilize the charging system which requires the addition of an ordinary motorcycle voltage regulator to charge an onboard 12V battery.

The ignition consists of the coil (usually located above the carburetor) and the magneto (located inside the front of the engine and is not visible).  The magneto supplies a +70VDC pulse to the primary wire at just the right moment (a little before top dead center of the piston).  The pulse is greatly amplified by the coil and becomes the +15,000V at the spark plug that ignites the fuel/air mixture inside the cylinder.

The magneto and charging coils at the front of the engine are very durable and rarely need attention.  It is the wiring from the magneto to the coil AND the coil connections to ground and the kill switch circuit that cause the most problems.

Periodically, examine the wiring and be certain that each connection is solid and that there are no broken or loose wires/connectors.  Be certain the male and female connectors are fully pushed together.

What is important are the connections of the ignition coil.  If any of these are not connected properly, the ignition coil will not function and there will be no spark.  Please refer to the schematic above regarding the following information:

1. The black secondary wire with the spark plug boot must be firmly connected to the spark plug.  The other end must have a secure connection to the coil.

2. The black wire labeled "A" must be grounded to the engine.  The coil will not work if this wire is loose.  In fact, pilots may notice a shock through the metal parts of the throttle cable including the kill switch if they attempt to start the engine with this wire unconnected.  This wire is the ground wire for the coil.

3. The blue wire labeled "B" is the primary wire of the coil and is connected to the magneto on the front of the engine and to the kill switch.  The wire labeled "C" (it can be any color) is the one connected to the kill switch.

4. The "E" & "D" connections are for the voltage regulator and are not used unless there is a battery.

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