Motorcycle Repair: honda 74 MT 125 Elsnor, primary resistance, rust free

Question
My son has this bike and it ran last yr. We got it out of storage this week end and it has very weak spark. Can you help us go in the right direction. Have had the coil tested and it has 6 ohms resistance. Could it be this or the condenser? Do you know what the stator resistance is? Thanks in advance for your help.

Answer
Chris, magneto ignitions need very clean point contact faces to ensure maximum spark. After that they need to be adjusted so they just OPEN at the F mark alignment of the flywheel to the index mark. If the points faces are deeply pitted, then the condenser may be weak and need replacing. Also the inside of the flywheel, where the magnets are located must be rust free and shiny.

I don't have specs for this model, but 6 ohms sounds high to me for primary resistance. Most battery-operated DC coils have about 4.5 ohms when used with points/condensers. Electronic ignitions have about .5 to 2 ohms on the primary side. The stator resistance should be very low readings and no connection to the grounded stator frame.

Check your spark plug cap for excess resistance. If it has a resistor cap, the reading should be around 5k ohms.

Make sure that your electrical connections from the magneto to the ignition switch and kill switch are all clean and tight. The ignition switch grounds the ignition when you turn it off. Disconnecting the switch should allow it to be ungrounded for a maximum spark test, if it is a suspect item.

Bill Silver