Problem with JD 620

I have a JD 620 that ran fine but now only fires on an attempted ignition but will not continue to run. I changed the wiring harness, changed the points and plugs, and cleaned the Carb before the problem appeared. I even timed it before this problem arose. The tractor started fine several times and ran fine for about 50 min and then died not to start again. It will fire when I try to start it but it will not catch and run. I am at a lost of what could be wrong. Anyone ever run into this problem or have an idea of what is wrong?
 
Do you have spark? If not try the simple stuff first, clean the points with a dollar bill. If you have spark, then look to the carb.
 
If it tries to start when you let up on the key, it may be a voltage dropping resistor in the ignition circuit. I don't know anything about your model tractor but that could be the trouble.
 
Id check the ignition ballast resistor and all its wiring and terminals......It should be around 1.5 to 2 or so ohms and drop around 5 to 6 volts thus leaving 6 volts on the 6 volt coil. When the starter switch is depressed its by passed but otherwise its in the series ign circuit between switch and coil.

John T
 
Like the other guys said it's most likely the resistor, a two inch long ceramic thing that's behind the dash. Run a jumper wire around the ballast resistor. Just clip one end on the input side and clip the other end on the output side making sure both ends have good contact, or take both wires off and clamp them together. If it runs after you let go of the starter pedal its the resistor. Also it could be there's no power getting to the resistor from the switch. If the resistor is bad you will want to replace it before you run it much it because bypassing it will burn your new points in short order. Jim
 
You didn't say you changed the condenser. If not, they can cause all kinds of symptoms when they go bad. Another thing I just had happen to me tonight on mine. Ran fine last fall when I parked it but it fired once and then quit when I went to start it tonight. I ended up draining the gas and taking the fuel bowl shutoff out of the tank. It wasn't letting gas to the carb. I took it apart and found some gung around the pin that lets gas to the carb. Ran like a top after that.
 

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