My guess would be carburetion...

Not sure if i'm up on the play with this story. But the last video where it only just runs sounds ignition like points are miles too wide &/or plug way too wide, maybe both. What's been going on. Have you been altering points out of range. Going back a page or two there's a video of it reving clean to the point of being rich & safe at max revs, just maxing out a bit rich on the main jet. Not forgetting the tiny Oring but if it was 'that' it'd be a lot richer & limited--i guess depending how bad it's leaking fuel past to bypass the main jet. But talking the curren vid where just starts then misfires & stumbles--reffer to my first sentence.

If nothing was changed or "fixed" recently, put in a new properly gapped spark plug.

Did you bleed the oil pump to get all the air out of the lines? It will run ragged, as the mixture it is burning will not be consistent with air in the lines. Do you have at least a half tank of oil while you are trying to solve this problem? You don't want it to be gulping air through the hose from the tank to the pump.

Flywheel slipped

cliff

Thanks for playing everyone, I think that I've found our issue. See if you can guess from the first video and then you'll see in the second. I think it's pretty obvious what I need to replace, no spoilers here

photos.app.goo.gl/mN113o9sAYwA1oD3A

photos.app.goo.gl/8Lq73UDyNQCRMtDc7

Also thanks for the reply Mothersbaugh, I did in fact bleed and purge the lines thoroughly, especially since I did the test where you rotate the pump 200 times to check oil output at least 3 times lol. Good to check though, I almost didn't check that before!

Yamaha have black oil lines so we won't worry, & never a problem providing oil in the tank.