Big problem in 4020

Diesels don't do that. Perhaps modern ones with a lot of electrical computer controls, but olderones like the 4020, once running, only require fuel---you can run them just fine with the electrical system switched off. This sounds like a GAS tractor. When the engine idles below 1500 rpm, the generator or the alternator(whatever it has) are not puttin out enough juice to run the electrical system or charge the battery. Hence, it will start with a jump from another battery or from a "booster", and as long as the engine is running fast enough, the generator/alternator is producing enough juice to power the the distributor and keep the engine running. Below 1500rpm, and with a weak/dead battery, it doesn't produce the necessary volts and amps and the engine dies.

Check the battery first, at someplace that provides load testing. If the battery checks out, check the belts on the Gen/Alt. If they are loose, tighten them. Next, I'd have the Gen/Alt TESTED, the same place that tested the battery can also do this. I'd also check the voltage regulator at the same time I had the rest tested.

Just my thoughts.

Good luck!

I suspect that in tractors FAR too new for me, the modern ones with computer controlled fuel systems and electronic governors just might have to have electricity to work. However, in at least the models I have, the fuel system is entirely mechanical---mechanical fuel pump included.

None of my diesels would be susceptable to cutting out at low rpms due to not having a sufficient electrical currant. However, my statement about a gasoline engine fits his symptoms---a generator that wasn't putting out a charge, coupled with a depleted battery would deprive the gasoline ignition system of the currant it needs to produce a spark, and of course the engine dies. Diesels are COMPRESSION ignition. No fuel will cause one to die, but not a lack of volts. That is why they require a fuel cut off mechanism to shut them down. You have to pull out the fuel stop knob to make them die, just switching off the key won't do it.

FWIW.

Frank-in-Tallahassee
70D // 855