Two Kawasaki Engines that Dip and Surge at Idle

I have two pieces of equipment with Kawasaki V-Twin engines and both are not running to my satisfaction. They seem to dip and surge at idle, particularly at startup. It seems to me that they might have the same problem, but I can't be sure. I have a feeling that both are recovering from instances of "the ethanol in the gas" that occurrded in their past, but I don't know the history of the 18 HP well enough to be sure.

Rather than try to describe what they are doing, I took some video (although the audio is what's important)

A 15 HP Kawasaki on a DR Brushmower
https://youtu.be/xO2dHiSzG5s

A 18 HP Kawasaki on a Johne Deere GT235
https://youtu.be/Y9771_KnhVc

I would appreciate any input on things to check. I pretty much disassembled and reassembled the carb on the 15 HP last summer and it didn't have any effect - good or bad. I will certainly post my findings if I figure out how to fix this issue.

Thanks,

Steve