Ford 9N intermittent spark, won't run

[JRP3]

6 Volt positive ground system, parked it about a month ago, now it will only fire for a second if at all. Put a clamp on timing light on the plug wires and only occasionally get a flash when cranking. Put a test light between the coil and ground, it lights when the ignition is on and flashes when cranking, so I'm assuming the points are working. Volt meter between the coil and battery ground shows voltage fluctuating when cranking between full battery voltage and about 2.5V. Coil is about 3 years old, tractor hasn't seen much use. Sanded the rotor, cap, and points even though they didn't look bad. Haven't tried hot wiring from the battery to the coil yet but I guess that's the next step. Any other ideas?

 

[RickB]

Check the ballast resistor behind the dash.

 

[JRP3]

What readings should I get?

 

[RickB]

Resisted voltage to the coil should be about 4 volts with points closed.

 

[JRP3]

So when I was reading the coil voltage while cranking and it dipped to 2.5V that was too low, or is it not accurate while cranking it?

 

[RickB]

I'd call it low. It should fluctuate between 6 and 4.5 while she points open and close, dependent on voltage drop caused by the starter's current draw.

 

[Roadworthy]

Clean your battery terminals well, as well as the connectors that attach to them. Tighten securely. Follow the ground to the frame and be sure it's clean and tight. Any voltage drop at any of these points is too much voltage drop. If it still won't run check the point gap and the timing. Do you have any moisture or cracks in the distributor cap? Are you sure the rotor makes good contact with the center of the cap? Are you sure your condenser is good? Be sure the points are tightened down securely.

 

[John0829]

Jumper around your key switch, that has always been a weak part of the ignition system.

 

[ROUSTABOUT]

6 Volt positive ground system, parked it about a month ago, now it will only fire for a second if at all. Put a clamp on timing light on the plug wires and only occasionally get a flash when cranking. Put a test light between the coil and ground, it lights when the ignition is on and flashes when cranking, so I'm assuming the points are working. Volt meter between the coil and battery ground shows voltage fluctuating when cranking between full battery voltage and about 2.5V. Coil is about 3 years old, tractor hasn't seen much use. Sanded the rotor, cap, and points even though they didn't look bad. Haven't tried hot wiring from the battery to the coil yet but I guess that's the next step. Any other ideas?

CONDENSER

 

[Chilliwack Murray]

As the previous poster said… Condenser.

Disconnect it and see if you get spark.