My vote would be possibly a weak return spring, or perhaps a cable that is starting to disintegrate, hanging up inside its jacket.

So it sounds like there may be 2 issues. 1] The spring rather than the clutch itself which you pretty much discovered . 2] the hopping. On my 87 244 M47 it turned out to be the rubber flex disk was cracked and plain worn out. It is an overlooked part, you might carefully inspect it for cracks etc. that would make it deform under load resulting in the hopping. If so, the part is in the $50 range.
--
1988 245A. Past: 1979 245A; 1987 244 M47; 1971 164E

MAybe the Cable is a bit goopy on the end so it does not fully engage the clutch. I would try and adjust the clutch a bit.turn the nut on the cable Clockwise about 1/2 turn and see what happens.
The Jumpy feel Might be Torque rod bushings. Bad 'U' joints might cause a bit of a jumpy feeling but if the Caps were broken on a 'U' joint, it would feel jumpy until you got to about 20 MPH then level out.

how close to the floor is the clutch engaging? I know mine are usually closer to the floor than the start. If the cable is adjusted wrong to where its engaging too soon it might be adjusted too tight. On the other hand if a clutch engages by pressing the pedal hard into the floor its too loose.