I’ve got a good-running little TO-20 that my parents (in their 80s) and I found in Tilene KY last spring. Its been converted to 12 volt with a one-wire alternator setup. After purchasing it I had an experience tractor mechanic do an ignition tune up…points, plugs, condenser, rotor, dist. Cap. He also rebuilt the car. Last week the weather turned cold and rainy here in Tennessee. A few days later when I tried to start the TO-20 it was not getting fire. All summer long it’s been starting and running like a top. What would most likely cause it to stop firing and can you suggest a good method for trouble-shooting and finding the cause of the loss of fire? Just to be clear, it turns over just fine and I’m confident it’s getting fuel. The way I determined the lack of fire was by pulling off a spark plug wire, inserting a screwdriver and holding it very near the plug while cranking on the tractor.
There are a number of possibilities. I would start by removing the distributor cap and wiping up any moisture inside the cap and inside the distributor. Check the cap to see if there are any cracks or if there is moisture or corrosion in the towers of the cap. Check the tower on the coil too and clean the towers as needed. A pencil eraser usually works well but they actually make a tool to do this. If that does not get it started, use a test light to see if you are getting power to the primary side of the coil. With a 12 volt system, the coil should be 12 volt and the battery should be wired with the ground cable going to the negative (-) terminal. The coil should be wired with the (+) terminal connected to the wire going to the key switch. With your test light lead clipped to ground, touch the probe to the plus (+) terminal on the coil and turn the key on. The test lamp should light. It is doesn’t you should check the ignition switch and wiring. Then, connect the test light lead to the positive terminal of the battery and the probe to the terminal on the side of the distributor. Engage the starter and turn the engine over. You can do this with the key on or off. The test light should go on and off as the engine turns over and the points open and close. If the light does not go on and off, you have a problem with the points or condenser. Try cleaning the points using a slip of paper, With the cap off, turn the engine over until the point are closed and then move the paper back and forth between the points to clean the contacts. Recheck with a test light and if it does not go on and off as described above, check the point gap and reset if needed. Next replace the condenser and try it again. Next the coil wire and try again. Then try a different coil. I suspect there is moisture in the cap or the points have oxidized a bit but corrosion in the tower is also a good bet.