JD 520 fires but won't run

Six-volt ignition systems don't have ballast resitors, so we can rule out a bad ballast resitor.

You say you have a spark at the points, and fuel to the carburetor . . . do you have spark at the plugs and fuel in the cylinders? I suggest you pull one of the plugs and take a look . . . is it damp with fuel? Next, reconnect the secondary ignition wire to the plug, set the plug down on a grounded surface, and crank the engine while watching the plug gap . . . do you get a spark for every engine revolution?

If you have both fuel to the cylinder and spark at the plug the engine should want to run (assuming that there is a reasonable amount of compression) if the plugs fire near the top of the compression stroke.

One last thing: The primary wiring of a six-volt Kettering ignition system is pretty straight-forward. A wire runs from the not-grounded battery terminal to the ignition switch. A second wire runs from the ignition switch to one coil primary terminal. A third wire runs from the other coil primary terminal to the distributor, where it connects to the not-grounded point and condenser.

When the ignition switch is in the ON position, electrical potential (voltage) is supposed to flow from the battery to the switch, through the switch to the coil, through the coil to the not-grounded point. When the points close, current flows from the not-grounded point through the grounded point to ground . . . and stops flowing when the points open again.

John

After your replace and gap the points, do this. Have someone try to start the engine while you spray carb/choke cleaner directly into the carb throat. If it starts and runs even briefly then you have a fuel delivery problem. If not, you have an ignition problem.

Without knowing the history of the engine, my best guess is that the static ignition timing is off. If you don't have the correct spec in front of you, any tractor engine will start and run with the timing set at 0deg BTDC (straight up).

Yes, a bad ignition resistor will fry the points. You can check with your DMM. You should see 9-12V at the coil (ignition side, not distributor side) with the key in the "run" position. In the "start" position, you should see 12V. You can then pull a plug wire, stick a screwdriver blade in the plug wire, and with a gloved hand, hold the other edge of the blade near the top of the plug. If you have no spark, you have an ignition problem.