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Coil Check

B

Bud W

Member
OK , I have 6 volts to my coil but I don't seem to have juice to the plugs. New points and condenser. If it helps sometimes the tractor ( Super C )will start and run and then just shut off like you pushed the switch in. Could this be a coil problem? How do I check the coil?
Thanks--Oh and by the way it has fuel and fuel runs out the carb drain when I open it.
 
It sure sounds like it. Use a substitute coil from something else to try it out. Junk yards are your friend. 60s or 70s ford up to 74. Jim
 
With the ignition on, take your coil wire. The one that comes out of the center (looks like a spark plug wire) and ground it to the block. when you do that it should have a hot spark and a snap if it"s working.
 
If you ground it to the block, it will not spark. To test it there must be a 1/8th inch gap. and be careful to hold it with insulated pliers not wet gloves. Ignition on and out of gear and cranking. Jim
 
Get your wife to help you have her hold the bare end of the coil wire in one hand while leaning on the tractor with the other. You sit in the seat and do what you would do like you were trying to start it. If this creates a lot of noise, mostly profanity you will know the coil is working. If you have to make your own meals it means it is working really good.
 
Hot wire it. As in run a wire from the ignition side of the battery to the ignition side of the coil. Start it up and see if it shuts down like is has been doing to you. If it does not then your problem is from the coil back. If it still dies on you then it is from the coil forward but not likely to be a bad coil unless it is very hot to the touch
 
When it stops check the volts at the coil as you could have a bad ignition sw. Ive seen that happen tractor runs fine then acts like the sw is turned off ended up being a bad sw.. so 6v wasnt going to the coil. Those sw can be intermittent.
 
OK this is getting wierd. I just rechecked the votage to my coil and its a full 12 volts. This tractor is converted to 12 volts with the 12 to 6 volt resistor and a 6 volt coil. Is it possible for the resistor to fail sending 12 volts through? I would think if they fail you would have an open condition but I checked it a half dozen times and I have full battery voltage on my coil. Now with 12 volts to a 6 volt coil would this keep the tractor from starting???
 
You will get 12 V on the "coil side" of the resistor if the coil is bad, i.e. interrupted (open condition), because your volt meter has a very high impedance, while the primary circuit of the coil is just a couple of Ohms.
 
12 volt system and resistor, at input to coil you should see 12 volts with points open, 6 volts with points closed. Sounds like points are not making contact.
 
This is the correct interpretation of your measurement. If the coil is disconnected from the points, or the points are open, no issue. Jim
 
Thats what must be happening. Just rechecked everything and I'm thinking the problem is the switch and here's why. About half the time I pull the switch out and check voltage at the coil I have nothing. When I do have voltage it is either 12 volts with the wire to the distributor disconnected or "4 " volts. In either case the tractor will not start. I'm thinking with the bad switch I'm either not getting current flow at all and when I do there's too much resistence and the tractor will not start with 4 volts to the coil. Make sense?????
 
As old indicated. Use a jumper to go from the battery to the coil (temporary hot wire to make a direct connection bypassing the ignition circuit. Jim
 
THe cranking current draw drops the voltage in the battery to about 10 volts. The coil can stand 10 volts for 20 minutes, your starter motor and battery cannot take 20 minutes of cranking.
The resistor drops the voltage to 7 volts or so during operation (charging voltage is 14.2). not to worry. Jim
 
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