BASIC MOTOPLAT TESTING

Section 1: Identification

All early Motoplat ignition systems share the same basic features and operational characteristics. The most critical electronics are contained in the external ignition secondary coil, the lighting/ignition primary coils are contained in the stator assembly. There are 2 basic Motoplat units found on vintage motorcycles, external rotor (flywheel) and internal rotor. The flywheel type, with lighting coils is the most common.  It is found on many MX and Enduro bikes. The internal rotor type has no lighting coils and is found mostly on competition MX bikes. There are several variations of the flywheel type. The information below will deal with them. I will list and describe the most common ones:

#1. I believe this is the earliest type commonly found. It has a replaceable diode in the stator. It is identified by a diode symbol (an arrow head pointing to the top of a T) on the front face and a large notch on the outer circumference (containing the diode) near the position where the wires come out. The wires going to the ignition coil have clear insulating covers.
6 volt lighting coils
Yellow wire, 35 watts {head light}
Green wire, 18 watts {stop light}
Red wire, 5 watts {tail light}
Black wire, trigger circuit to ignition coil small terminal
Blue wire, capacitor charge wire to ignition coil large terminal and kill switch

#2. Similar in appearance to #1 but no notch, although it still has a diode in the stator. The wires going to the ignition coil have clear insulating covers. The wire colors and wattage values are slightly different.
Yellow, 35 w {head light}
Green, 21 w {stop light}
White 5 w {tail light}
Black, trigger {small terminal}
Blue, capacitor charge {large terminal} and kill switch

#3. Similar to #1, however there are some important differences. It has no diode in the stator (it is has been relocated to the ignition coil), there is no notch, and no diode symbol on the face of the stator. The easiest way to identify it is by the red insulators on the wires that go to the coil.
Yellow, 35 w {head light}
Green, 21 w {stop light}
White, 5 w {tail light}
Black, trigger {small terminal}
Blue, capacitor charge {large terminal} and kill switch

There are 2 types of ignition coils for Motoplat, as follows:

Black spark plug lead. This type has no diode in the coil.
Red spark plug lead. This type has a diode in the coil.
The black wire coil can only be used with the early (#1 & #2) stators with the diode. The red wire coil can be used with all three types of stators.

Section 2: Testing

I will describe the testing procedures for the ignition coils first and then the stator testing procedures. It isn't necessary to remove components from the motorcycle, but if on the bike testing indicates a marginal (or faulty) component it is recommended that the part be removed and retested. All tests should be carried out with an Ohmmeter with a capacity of 0 to 10,000 ohms or greater.

#1. Testing ignition coil with the Black spark plug cable.

Remove both stator leads from the coil, and disconnect the spark plug lead from the plug. Set the Ohmmeter to read values from 0 to 50 ohms.  Connect the test leads of the meter to both flat terminals of the ignition coil. You should get a reading between 20 and 30 ohms. If the reading is lower (0 or near 0) or higher (50 ohms or more) the electronic system is defective.

To test the electronic circuit in the coil set the measuring range of the ohmmeter to 1,000 ohms. Connect one test lead to ground and the other to the large terminal on the coil. Charging of the condenser in the electronics should cause a brief deflection of the
ohmmeter's needle, and then the needle should return to infinity. Reverse the test leads. Again the needle should briefly deflect and return to infinity. Repeat this 3 to 4 times. If the pointer does not go back to infinity but remains on another measuring value the
electronic system is defective.

To test the secondary winding of the ignition coil, connect one test lead to ground. Connect the other test lead to the wire in the spark plug lead. You should get a reading between 7,000 and 9,000 ohms. If so the secondary winding is in order.

#2. Testing ignition coil with Red spark plug lead.
The electronic circuit cannot be tested with an Ohmmeter.
The secondary windings can be tested as above.

#3. Testing the stator WITH diode (#1 & #2, clear insulators and diode symbol)

Disconnect the black wire from the ignition coil. Disconnect the blue wire from the ignition coil and the kill switch. Connect one lead of the ohmmeter to ground. Connect the other lead to the blue wire. Note the reading. Interchange the test leads and note the second reading. In one connection the reading should be infinity, in the other, 3,000 to 9,000 ohms should be indicated. If a reading of very low resistance (0 to 50 ohms) is obtained in both cases, then the diode is defective. If a reading of very high (over 15,000 ohms to infinity) resistance is measured, there is an interruption in the stator plate.

#4. Testing the stator WITHOUT diode (#3, no diode symbol, red insulators in coil leads)

Disconnect the black wire from the ignition coil. Disconnect the blue wire from the ignition coil and kill switch. Ground one test lead from the ohmmeter. Connect the other lead to the blue wire. A resistance reading between 140 and 180 ohms indicates the charging coil is in order. Next connect one test lead to the black wire and the other lead to the blue wire. A resistance between 16 and 24 ohms indicates the trigger coil is good. A low reading (less than 15 ohms) indicates there is a short in the trigger coil.

Whenever an electrical problem is encountered, always check all terminals and connections to ensure they are clean and tight. If the problem persists or reoccurs, you should THOROUGHLY inspect all wires, terminals, and connections. You should disconnect, inspect and clean every junction. Check each wire for kinks, nicks, and abrasions. It is also a good idea to check each wire with an ohmmeter to be sure it is not acting as a resistor. Its also very important to ensure all components are properly and thoroughly grounded. Again remove each component, inspect and clean, before reinstalling it. Most problems can be traced to a poor connection or faulty wire.

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