If you haven't used it for a bit the shaft may be stiff. Put a bit of WD 40 where the shaft meets the spool area, leave it a while and gently rotate the spool area with your hands and it should start to move. That should cure it. Another thing that will stop it moving is grass, string or wire wrapped around the top of the spool area. If both of those fail the shaft may be wrecked but unless you have used the wrong fuel that is unlikely.
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Mcculloch 2818 Runs fine but spool will not spin?
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