<<Does it blow out any black smoke when it chokes out? >>
Yes, it does. It seriously just like you choked the carburetor for a couple of seconds.
Doesn't that imply that it's being periodically flooded with fuel to cause that problem?
Just guessing, but if the fuel pump was increasing fuel line pressure periodically perhaps that might cause this kind of problem. Perhaps the fuel pump is supplying a little too much fuel pressure and that is reflected in the periodic flooding, with the flooding relieving the excess pressure for a few seconds. Can you temporarily eliminate the fuel pump and feed fuel by gravity as a way of testing that kind of theory?
I'm wondering if you could try partially pinching off the fuel line to the carburetor to see if that affects what's happening. Restricting the fuel line might reduce the fuel pressure and cause the engine to run normally if that's the problem. I might try putting a screw clamp on the rubber fuel line and gradually tightening it to see if that causes the engine to even out at some point.
A dirty fuel line float or valve seat that's allowing too much fuel to get into the carburetor some of the time?
And if others think periodic flooding of the engine might be causing this problem, you may need to spend a good deal of time with your engine to think of more things that could be causing the problem, and ways you can test those ideas to see if they are the actual cause of the problem.
I'm no Xpert. I'm trying to develop diagnostic skills on small engines that I don't have. So don't take these ideas too seriously. I figure perhaps I can develop some diagnostic skills by imagining possible causes of problems people are having and coming up with methods to test those theories.