jchamberlin
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- Jeremiah Chamberlin
For <font color="0000ff">charles hoffman (Choffman)</font> back on Monday, December 24, 2012 - 03:50 pm: If you haven't figured it out by now, there should be one wire from the engine that disappears down into the shrouding along with the spark plug wires --it is the "kill wire" for the magneto which, when connected to ground, kills the engine.
You didn't tell us into which model tractor you've installed the motor, but if the tractor was designed for a magneto-fired ignition system, then there should be a terminal on the ignition key switch that grounds out the "kill wire" when the key is in the off position. The terminal should be marked "M" for "Magneto" (or "Motor"). Again, if the tractor originally had an M18 or similar motor installed, the "M" terminal at the key should have a wire running out to the connector in the engine bay.
If your tractor did NOT originally come with a magneto-fired ignition, but instead used an ignition coil, then it has what is termed by MTD as a "Battery" ignition switch. With this arrangement, the key terminal marked "I" for "Ignition" carries 12 volts to the coil when the key is in either the Start or Run (or Run w/Lights) position and offers NO CONNECTION when the key is in the OFF position.
The easiest way to convert an ignition coil type tractor to use a magneto-fired engine is to install an interposing relay such that the positive 12 VDC from the key energizes the relay. The Normally Closed contact of the relay is then connected to the kill wire from the Magneto, and the Common contact of the relay is connected to a good ground.
Thus, when the key is in the ON position, the relay is energized, the engine can start and run; but when the key is in the OFF position, the relay is de-energized, the magneto is grounded out of the circuit, and the engine dies.
The problem you are experiencing is due to the fact that, unlike an ignition coil type ignition, a Magneto does not need external power in order to function --the motor starts itself when it is turned over-- the challenge (as you have discovered) is shutting it off.
Been There, Done That, have the T-shirt to prove it.
Edit: Cute One, Troy --I love it (Jeff, I want the spring assist)
You didn't tell us into which model tractor you've installed the motor, but if the tractor was designed for a magneto-fired ignition system, then there should be a terminal on the ignition key switch that grounds out the "kill wire" when the key is in the off position. The terminal should be marked "M" for "Magneto" (or "Motor"). Again, if the tractor originally had an M18 or similar motor installed, the "M" terminal at the key should have a wire running out to the connector in the engine bay.
If your tractor did NOT originally come with a magneto-fired ignition, but instead used an ignition coil, then it has what is termed by MTD as a "Battery" ignition switch. With this arrangement, the key terminal marked "I" for "Ignition" carries 12 volts to the coil when the key is in either the Start or Run (or Run w/Lights) position and offers NO CONNECTION when the key is in the OFF position.
The easiest way to convert an ignition coil type tractor to use a magneto-fired engine is to install an interposing relay such that the positive 12 VDC from the key energizes the relay. The Normally Closed contact of the relay is then connected to the kill wire from the Magneto, and the Common contact of the relay is connected to a good ground.
Thus, when the key is in the ON position, the relay is energized, the engine can start and run; but when the key is in the OFF position, the relay is de-energized, the magneto is grounded out of the circuit, and the engine dies.
The problem you are experiencing is due to the fact that, unlike an ignition coil type ignition, a Magneto does not need external power in order to function --the motor starts itself when it is turned over-- the challenge (as you have discovered) is shutting it off.
Been There, Done That, have the T-shirt to prove it.
Edit: Cute One, Troy --I love it (Jeff, I want the spring assist)
