Hi: Have timed it numerous times in 30 years, have followed the instructions you give, I made a spark plugIf that is the case then you can check it using the method I described recently. Plugs out, tappet covers off, rotate engine with rear wheel and watch the rear inlet valve open, then close, bring piston up to TDC and then see if the points are just about to open. If not then do the same for the front cylinder. If both are wrong then it is probably a 360 degree problem. If one is correct then possibly it is timed up on the wrong cylinders. There is nothing special about any of this. Just think back to how four stroke engines work and go from there.
stop years ago, points are opening 35 degrees BTDC.