i recently bought a Deutz-Allis 1920 ultima. it has the 20 hp kholer Magnum engine. when i am mowing it seems to dog down in some of the thicker grass i mow in the yard. also when i shut it off or it stalls out i have to let it sit for about 10 minutes before it will restart, and when it does it blows out black smoke on start up which i am thinking is raw fuel because the same thing happens when i pull the choke while it is running. when i first start it it starts right up. any help on this would be appreciated as i am not familiar with the magnum engine.
Jason, this story sounds kind of familiar. My M20 has had some of the same symptoms.
The first thing you need to know is whether you have good compression in the cylinders. You should do a leak-down and compression test to find out. That was the problem with power loss in my engine. It needed rings and I also had the valves re-ground.
The hard starting when hot is something that would be aggravated if you have low compression. My Magnum never started as well hot as it did cold, but it got worse as the engine lost power. This could also be caused by other things, so you might clean the carb to see if that helps. Check the spark plugs. The magneto could be going bad and giving a reduced spark when hot. You could pull the plug wires when cold and observe the spark (put a bolt or something in the plug boot and hold it near ground while cranking), then do the same thing when it is hot. Should see the same kind of spark. (Try to do it cold and hot in the same way and with the same lighting; or maybe you have a tester for this). Also, if you have the engine out, you should check the magneto-to-flywheel gap to see if there is a problem there.