2166 with Surging idle
 

I have a cub cadet 2166 with the Kohler 16 hp engine with 766 hours. My dad passed away recently and he kept it maintained quite well. It just started running rough on me. It starts fine but the idle goes up and down not steady. Due to the hours on it I replaced the carburetor, the fuel pump, the fuel filter, and the spark plug. It gets plenty of spark at plug. Battery is newer and fully charged. This did not change anything. I can’t tell if starved for fuel or too much fuel. It has never right with choke wide open. Always closed 1/4 to 1/3.
What else can I check here?

Thanks

Bub

In other words.... engine runs fine WOT and no choke? With that thought in mind:

Not familiar with 2166 engine....Does your carb have low idle mixture screw? Adjust for more fuel.

Or.. possible intake leak/vacuum issues.