Welcome to the new Wizard Outboard Forum.
WG4 and WF4 are similar if not the same powerhead AND they use same F 189 magneto & flywheel
Mercury Mark 7 uses a similar but different Phelon ignition/flywheel with torque specc
Remove all trace of grease, oil and grime from tapers in flywheel hub and on crankshaft.
Torque to factory spec...too little may allow flywheel to work loose...to tight may
split the flywheel hub.
If tapers are rough or rusted it may be possible to use valve grinding paste to lap the tapers to match. Some would say lap any flywheel not original to the crankshaft.
Main thing to keep in mind is the taper does the work of holding flywheel and crankshaft together. Key and keyway are there to locate not hold. Correct torque
and dry clean taper create the lockup.
Simple things are not difficult to do the right way , but, often are done the wrong way or not at all.