The PTO clutch on the tractor is electro-magnetic and takes a lot of current to operate. If you have a low battery condition this will stop the tractor because you don't have enough voltage to run the ignition system with the PTO turned on.

First, check the battery voltage with the tractor off. You should have about 12.75 to 13+ volts (depending on the age and condition of the battery).

If the battery voltage is low you could have one or more of the following problems:

1. Old battery that will not hold a charge - needs replacement.

2. Bad voltage regulator - battery is not being charged and electrical system is running on low voltage when the engine is on and the PTO draws enough to shutoff the tractor.

3. Bad stator - battery is not being charged.

Of the three possibilities - 1 & 2 are the most common. A bad stator is the least likely but, you can easily narrow this down.

Start the tractor and check the battery voltage. If the stator and voltage regulator are working correctly, you should have 14+ volts at the battery. If you do not have 14+ volts with the motor running, then the battery is not being charged - and there is probably not electricity being supplied to run the electro-magnetic PTO clutch + ignition.

You can sort this out by starting the engine and pulling the connector from the voltage regulator and looking for AC voltage using a multi-meter. I do not know the exact terminals on that engine - but, you should be able to find a service manual on line in electronic format for about $8.00. Otherwise, you can do this by a process of elimination. Put the probe in the top left contact and check the other contacts sequentially. What you're looking for is about 30 Volts AC from the stator. Then go to the second contact, repeat, etc. If you don't find the voltage - bad stator. This really isn't as likely as a bad voltage regulator.

Voltage regulators have diodes in them and other semi-conductors and after being continually exposed to heat, vibration, etc. - they go bad.

So, check the voltage regulator with a multi-meter on the Ohms setting. Most of the resistances should be in the 4.5 mega-Ohm area. If you find opens or low Ohm readings between contacts on the voltage regulator - it needs to be replaced. My guess - it's the voltage regulator and you will find several "open" conditions.

I just replaced the voltage regulator on a John Deere garden tractor because the PTO would not stay engaged and the battery was always low.

If you find the voltage regulator is bad, in your case I would replace both the voltage regulator and battery if the battery is over 2-3 years old as constantly running it in a discharged state has probably compromised the battery's ability to hold a charge.