I don't think you can "work it too hard" no matter what you do, other than running it out of oil, running it too lean or letting it overheat due to a mouse nest inside the tins. These engines are basically bullet proof.
J-Mech's probably nailed it on the fuel issue. Next time it tries to die, pull the choke and see if that helps momentarily. If it does, they you've likely confirmed a fuel supply issue. Running lean can cause a knocking sound if I'm not mistaken.
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