Ferguson te20 started running like crap!

What to do, next? Ferguson TE20 Tractor was parked for the winter, was running fine, maybe a little rough when I shut her down last fall, started up fine, ran it for 15 minutes, then started losing power and backfiring, added 5 gallons of new gas along with Lucas gas additive, the remaining gas was a year old but it had risline treatment, changed oil and added marvel mystery oil to crankcase, it s started running better, but after it warms up it dies and won t start until it cools off, any advice will be appreciated, my wife and I are retired put up ten cords wood every year to get us through the winter, so Thankyou for taking the time to read this and helping. Also I put in a new igniter 12v system in a couple years ago.

Coils breaking down do this . When hot a small fracture in the windings opens up and reduces the coils ability to produce strong spark . When cold it closes up and works well until it warms up again .
Otherwise in a UK built tractor with a Standard Motors engine there is a filter inside the tank . You must remove the fuel tap to see it . It is an upright cigarette filter bronze gauze which either clogs or crumbles into the fuel out let . If it's still there remove it and throw it at your worst enemy.

Start with checking the spark, should get minimum 1/4" spark to ground at the plug end of each wire. Not at the cap, but at each plug.

If good, check the fuel delivery to the carb. With the engine off, fuel valve on, have a clean glass ready, remove the drain plug from the carb, catch the flow. It should have a full flow, slowing as the bowl empties, but not slowing to a drip or stopping. If it does slow or stop, trace the problem back toward the tank. There may be a screen in the inlet fitting of the carb, and one in the tank. Look at what was caught, if cloudy it is water contaminated. If dirty or rusty the tank will need to come off and be rinsed and dumped out. If severely rusted it may need to be replaced. Whatever is in the glass will also be in the carb. It may need to be eased apart and cleaned out.

But the best diagnosis is done when it is failing. Be ready to check the spark and fuel delivery immediately when it fails.

A properly operating coil will be about the same temperature as the surrounding components. If too hot to hold, it is getting too hot.

Be sure the gas cap is vented. Try opening it when it fails.

Be sure the fuel line is routed as far from the exhaust manifold as practical. The original fuel line would have been steel. If a copper line has been used, it is more conductive than steel and promotes vapor lock.

If there is an inline fuel filter, that can be too restrictive for a gravity system. With a clean tank, the original screen and separator are sufficient.