I found the following reply to a very similar question from EE Bota (RIP) he posted several years ago:
Most times it is a partially clogged carb jet, or the float level is too low, or a leak in the path from the carb to the head.
But I don't like how it happened to you all suddenly. So, make sure that the fuel tank is vented, and gas flows freely to the carb. I'd literally start at the tank and work my way to the head. The closer you get to the head, the more the work picks up, but you may find the problem at the tank, the bowl (if present) the fuel line, the inlet strainer to the carb. If you get to the carb, try spraying carb cleaner around the joints where the carb attaches, etc to try to find carb/ manifold leaks. All that is still easier than going into the carb.
Sometimes I can fix a carb while still mounted, but usually I have to remove it to repair it. Hopefully, you will find something simple without having to go into much.
I noticed that it has an oil bath air cleaner. I'd service that cleaner to make sure the correct amount of oil is in it as that has a slight choking effect all on it's own that the carb is tuned to accept. Low oil or missing filter components will breath easier and alter things a bit.
From the same thread another reply:
If it needs the choke to run, there's a clog in the main jet. I would assume that the tractor has either sat for a while and you have some varnish in the jet or that the fuel filter has let a chunk of junk into the fuel bowl and subsequently clogged the jet. In most cases, it shouldn't be too difficult to pull the carb off, pull the float bowl, and clean out the main jet and passage. The worst thing that you can do is jsut start turning random screws. Unfortunately, turning screws can mask a problem, but can't solve it.
Before buying a new one....take the old one apart and clean it. If there's a screw with a passage behind it, count the number of turns it takes to tighten it from the seat. When you reinstall it, tighten, then back it off the same number of turns. This should keep your settings the same.
The only real reason to replace the carb would be if the bushing that the shaft is on is worn too badly. Always rebuildable. Carbs run on some basic airflow and fuel flow principles. A better understanding of those is a better key.
Another possibility is a vacuum leak.
