HW77 springy underlever

[TonyL]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

I had a 97 with the same problem,yes indeed, a cocking arm like a dog's hind leg

Yep, agree.

Also, guessing it's a Mark 1, check that the sides of the foresight unit / underlever retaining recess aren't damaged and also that, if the unit has ever been removed, it's securely fastened (Loctited) in its rearwards most position.