You don't need much spring tension on the handle. What keeps it down is the compression on the lower spring when it hits the attachment plate, and the handle keeps moving until it hits the stop, (usually adjustable) just over center. That lower spring is holding the pin tight against the QA plate.
The distance the pin goes down varies on different plates, depending on wear in the slot.
To raise the handle, you have to compress the lower spring a little as the linkage comes back over center and pulls the pin up to unlatch the attachment.
Compare this handle to yours, notice how it has been ground off to provide the over center stop when it is fully down as in their picture.
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