In Reply to: 24hp B&S engine surges at idle posted by NTP on June 14, 2018 at 04:00:41:
I would guess that the surge is caused by dirt and leaves sticking to the air vane governor and linkage. Most all of those motors have a governor that is blown by the fly wheel to throttle down the idle. When the idle gets low the flywheel does not blow as hard and a spring attached to the throttle overcomes the vane that restricts the throttle and gives more throttle. When it revs up the flywheel blows the vane that again over powers the spring and throttles it back.
You need to take off the shroud and clean the throttle linkages and spring and vane and pivot points for vane. You don't want to oil those parts because dirt will just stick to the oil and gum them up.