I have a Scotts by John Deere S1642 tractor mower. It has a Kohler CV16S-43526 engine on it with a Walbro carb.

The carb has something called a self-relieving choke on it with some sort of spring loaded mechanism between the choke cable and the choke plate/shaft.

The engine starts great, but runs really rough at any other speed than really slow. After a lot of investigation I noticed that the choke butterfly plate closes perfectly when the throttle lever is set into the choke range, but when you move the lever to the run position, the choke butterfly plate is free to move and kind of "flops" around. When I say flops around, I don't mean that the mounting screws are loose or anything, but the choke plate is so free to open an close that it gets pulled partially closed, then pops back open. Maybe a better term than flops is flutters. This pattern repeats all of the time, meaning it never stabilizes when the mower is at full speed, so the engine speed never settles down. This causes the engine to slow and surge, thus resulting the in throttle butterfly plate being opened and closed by the governor, and, thus, the rough running.

At slow speeds, the air flow past the choke plate seems to be slow enough not to cause the erratic action of the "very loose" choke plate.

Lastly, if I take the air filter assembly off and hold the choke plate in a fixed position, the engine runs smoothly.

Do you know if the choke plate on these self-relieving choke carbs should be that loose, or should it be wide open when the throttle lever is in the "run" position?