JD300 Keeps Stalling Under a Load

I have a 1972 JD 300 Industrial Tractor that has a 3 cyl gas engine and it keeps stalling out after running awhile when you put a load on it. Any idea what could be causing this?

Two likely things to check. #1 is a overheated coil. When they go bad they get very very hot. The second is fuel flow. A partial stoppage of fuel,
or a plugged gas cap vent will limit fuel flow. Jim

Need to do some basic diagnostics.

Stalling under load is almost always either weak spark or fuel starved. Best to have everything
ready to quickly catch it in the act when it fails.

Start with the ignition system. If any doubt about the plugs, replace them just to say you did.

You should get a blue hot 1/4 inch spark to ground at the plug end of each wire.

Check the points gap and condition, check the distributor shaft for side play. It must be tight or
the points will not stay set.

Feel the coil, it should not be uncomfortably hot to touch after a few minutes running. If it is,
it may be failing or has the wrong coil, or coil/resistor combination.

Next move to the fuel system.

Be sure the air cleaner is serviced and flowing freely.

Be sure the choke is fully operational.

Be sure the governor is functioning. With the engine off, dash lever set to fast, the throttle on
the carb should be wide open.

Check the gas cap, be sure it is vented. Even if it says vented, try loosening it just to see if it
is not holding vacuum.

There is a drain plug in the bottom of the carb. Have a clean glass ready, engine off, fuel tank
valve open, (engine idling if there is a fuel pump). Remove the plug and catch the flow in the
glass. There should be a continuous flow, not slow to a drip or stop. Look at what is caught. If
there is water, excessive grit, rust flakes, the tank and carb are contaminated and will need to be
removed and cleaned. There should be a screen inside the tank, a screen in the sediment bowl, and a
screen in the carb inlet elbow. Be sure these are clean and accounted for. Adding an inline filter
may cause flow problems with a gravity system.

If there is a fuel pump, route the discharge side to a container, crank the engine, it should give
a strong positive pulsed flow at about 2 PSI.

Check these things first, see what you find. Let us know...

If you are still having trouble after following the excellent advise already given you can check your power steering.

I had the problem once when the valving in the steering column was messed up and it caused the hydraulic pump up front to put a huge load on the engine.

Slower than normal cranking when you try to restart it is a symptom.

Turning the destroke valve on the font pump to take it out of the equation is a simple test for it.

Check timing. I've seen advanced timing cause that same issue. Start and run perfectly until under load, no lugging power just stall out.

Thank you everyone for your recommendations. The coil is hot when it does it, so I plan to replace it along with the spark plugs. I cant seem to locate a replacement coil based on the tractor model. Is this a part that is readily available or does anyone have a part number? If not, I will remove it from the tractor and see if I can find a number on it. Thanks!

Thank you everyone for your recommendations. The coil is hot when it does it, so I plan to replace it along with the spark plugs. I cant seem to locate a replacement coil based on the tractor model. Is this a part that is readily available or does anyone have a part number? If not, I will remove it from the tractor and see if I can find a number on it. Thanks!

JD 300 parts catalog says the JD part number is AT14385 (Prestolite 200627). Your local parts store should be able to cross those to the brand they have.

Good newsI replaced the ignition coil and it works great now and no longer stalls under a load. Thank you for all the advice!