I'm not sure what type of freewheel comes on the Zoot... if it has a visible lockring make sure it's tight and if you can take the crank off, take the lockring off (do that over a tray so you can catch all the bearings) and have a look at the pawls and springs etc. You might find some damaged pawls that you can file back to a healthy state. Next step would be to replace the freewheel but that involves being able to take the existing one off the cranks which can be a bigger challenge than getting the sprocket off!!