I only try and help and think I usually do. Anyone posting here for help will take advise for what it's worth.
I have no access to technical manuals etc. Only from experience.
No need to bad mouth anyone here.
Make sure your air filter is clean or not stopped up with dirt, there may be an adjustment screw on that carb , most don't these days. Guessing you have clean gas , that E85 stuff can make it run rough .
Might take the carb off and clean it up real good
Woodruff key's are there mainly to protect your engine drive assemlby, Why yours they usually shear when you hit something solid and keeps you from bending a shaft or other damage. If it happens again you'll need to dig further to find out why
There are seals and bearings in that gear box , It's a pain to rebuild but I've done a few, Be real careful when tearing into it - there are shims and gears and bearings that need to come off the drive and driven shafts and need to be re assembled in a certain order.
You probably have a jet plugged in the carb, pull the needle valve and the seat , there is a jet under there that has very small holes , easily plug with small particles , you should be able to see through every hole when you hold up to the light.
You can lap the valves with a little lapping compound, How does the compression stack up other than leak down ?
Carbon can score the cylinders and is very abrasive , side to side indicates worn valve guides and can be a cause for smoke / low compression lack of power etc.
If you got good compression and fire , that leaves only fuel as the problem, Timing is not an issue since it runs on one cylinder so concentrate on fuel delivery.
Depends on the type of meter you have , some sense a pulse from the magneto and read then , if it requires 12 volts then it should read as such when the key is in the On position
I installed one on my outboard and if I remember right there weren't any wires to hook up it just picked up a signal...
Pull the wires off at the connection , check both to ground - only one should read ground , engage the switch and see if you have 12 volts on the other wire , if test passes , re connect and engage the switch and listen to the PTO , it should click and engage.