This one has me stumped. This is a Kohler CV20S on a C&S Turf Tracker. It had been out of service for a while before I got it going last week. When you engage the starter, it makes a humming noise not unlike an arc welder. The engine will turn over very slowly, almost stopping when it gets to the compression stroke. I had the engine running (started on starting fluid) on Friday. It runs perfectly, drives perfectly. Ran up and down the street for half an hour. There is slack in the drive belt for the hydraulics, so that's not it either. I swapped out the starter for a spare - no difference. I disassembled the battery connections, removed rust, etc. - no difference. I disassembled the other ends of the battery cables, removed any corrosion - no difference. I disassembled the two rear engine mounts, removed rust down to bare metal - no change. I have 11 volts at the battery, 11 volts at the starter. I have continuity on the ground cable. I hooked it up to the battery charger, set for 12 volts & 50 amps. No improvement. What am I missing here?