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I’m new to this site and I know little about tractors and I do not own one. But my father owns a 1958 John Deere 620 and he is currently at his wits end trying to get it to run. He isn’t the most tech savvy person so I’m asking this on his behalf. He recently switched the generator out for an alternator and was able to start it up and drive it for 10 minutes afterwards. After that he has been able to start it twice but only for 4 or 5 seconds before it dies, then after that he has been unable to get it to start. He has replaced the main battery cable, condenser, switch, resister, points, resister (on the distributer), rotor cap, distributer cap, spark plugs, and the coil. (He has replaced the coil with a ‘hot spark’ coil and also tried to replace it with a standard coil, and neither has worked. And he has tried to replace the electronic ignition in the distributer but it didn’t work so he switched it back.) (I think he has replaced most of the wires with what looks like 16 gauge wire.)

Right now when you put a screw driver to the terminals on the coil and touch metal you get a spark for each terminal. When you try to start the tractor and you hold the coil wire there is no spark coming out of the coil wire. (I only know this from holding the wire end when there is an attempt to start the tractor.)

Also not sure if it matters but the tractor is running 12 volt battery as opposed to the dual 6 volt setup the tractor had in the beginning. (This was replaced long ago and has worked fine since.) The battery has been fully charged as well.

He has done everything that he can think of at this point. If anyone has any thoughts as to why this tractor isn’t starting, we would greatly appreciate it if you shared them.

Thanks,
 

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Try running it with out the resistor. If it runs problem solved. If the coil burns up, get a resistorless coil for a 1970 VW beetle. They should still be cheap as parts stores are trying to emptyy their oversurplus. The resistors when hot will often fail.

Also make sure it has good fuel flow. Bad fuel flow can make starting awkward
 

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My suggestion is to turn the engine until the points are closed, turn the ignition switch on, and use a voltmeter to check the voltage on each coil low tension terminal. You should see very close to zero on the lead to the distributor, and 6-8 volts on the other terminal.

Now turn until the points are open and check again. Should get 12v on both terminals.

Most likely, that will show the problem. If not, replace the coil.
 
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