I think I see something funny with that clutch. I think it's broken or damaged.
I agree, something looks off on that sheave down near the shaft.
Easiest fix, find a new clutch to replace it. It needs to be off a triple as the crank taper is different from twins. I learned this the hard way when I bought from someone who "knew what they were talking about". If the spring and weights are in good shape they could be switched into the new clutch if it has different ones in it that aren't correct for your machine. Beware on ebay since many sellers just put "fits 400, 440, 500, 600, XLT, XCR" lists everything without knowing. The difference isn't significant but since the twin taper diameter is slightly wider, trying to install a twin clutch on the triple crank will bind it on the crank seal and won't spin.
Or just go with a new powerbloc clutch.
You can always check the distance between clutches and the offset alignment. Center distance of the primary and secondary should be 12", the offset from the back of the secondary to the back of the primary should be 5/8" with no starter gear, 1"with electric starter ring. Take a straight edge at the back of the primary that reaches the secondary and measure the gap.
Check that the motor mounts are in good shape since if they're crooked or worn down the primary will be sagging lower or in the wrong place and may cause these types of issues.
But it really looks like there's something off with that sheave.