I have a 1985 Wheel Horse 417A 31-17KE01. When I pull up the lever to disengage the drive, the belt will continue to move erratically (slow, speed up, repeat.) I've attached a couple of pictures, and have a one minute video showing how it's operating... (this is a OneDrive link, if it's not working someone please let me know.) I wish I could provide more info in my post, but I don't know enough about what's occurring here to do so.
https://1drv.ms/v/s!AsmNVhojMf_GqAHdTKh3d5-0uFVI?e=30SyhH