I have a 16hp Kohler Engine on a Craftsman lawn tractor. It starts fine, runs fine, and has plenty of power. The issue is that when it is low RPM, the engine surges RPM up and down. It also does so at high RPM if not under load but is a lot less noticable.

I have rebuilt the carb making sure the openings were all clear. I pulled the aluminum plug and cleaned out the two holes. I replaced the plug. I also have replaced the needle valve and installed new gaskets. The filter is fine with a flow rate of about 1/4 gallon per minute.

Any help appreciated.

 

It is still a restriction in the carb. Not sure where. Get a twist tie from a bread bag and pull the wire out of it, then run it through all passages in the carb, including the holes in the side of the carb where the throttle plate closes against the throat wall. This is commonly where the restriction occurs. Also run it through the brass tube in the center of the carb.