I know this is an old thread but I'll add my experience just to archive it in case someone else is looking for help and like me gets here via Google search.
I have a 2017 TB 110 dump find with a B&S 550EX, 11A-A2BM711, 09P702-0144-F1, 140cc engine .....cheap mower but it's in great shape and has the bag. I found that mine was surging as a result of a defective auto choke capsule. I replaced the carburetor and even enlarged the main jet but couldn't get the surge to smooth out. My auto choke just flops around with no resistance in either direction.
If you're unsure where to look, just follow the rod that connects from the carburetor to the round device above the cylinder head area. I believe it's filled with wax and maybe a spring that reacts to hot and cold. When cold it allows choke and the opposite when hot. I bent the rod to take the choke off for now. On a properly running engine you would adjust the U shaped center of the rod. I'd order a new one but can't find a part number or picture for the auto choke anywhere. I'll stop by a shop this week and see what's available or if it starts easily as is will leave it like that.
Best,
Jay in MA