One of the more common problems I see when people are having trouble reassembling the clutch on a CB750 is misalignment of the splines of the pressure plate and the clutch center. It is not obvious by looking at them but, there are four ways to put them together depending on how they are rotated, and only one or two will work properly. It's easy to see when the parts are disassembled and on the bench.
This is how the pieces fit together:
Normally their respective splines mesh like this:
BUT you will find that if you rotate the clutch center by 90 degrees, the splines no longer line up properly:
Now, I don't know that this problem would cause your particular symptom, usually it's the opposite, the clutch won't grip because the pressure plate can't clamp down onto the plates:
Once you've found the orientation that works, mark one of the spring posts for future reference. Magic marker for temporary marking, or dimple it with a center punch for permanent reference.
So again, don't know if this could cause your symptom or not but it's worth check, just to be sure.
cheers
mystic_1
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