Thinking out loud here
Apologize if this is to Simple..perhaps something useful The kick resistance looks about right
for a tight engine. I jump upwards and on the way down kick it .
I had a friend trying to kick it he is over 200 pounds. He had problems.
There are like 2 positions the second one can be easier but mine prefers to start on the first.
Yes the valve play should be checked
I would try if it is possible to squirt in some oil at the top end at that time on relevant points.
I get the impression the ignition is a little off
can give the hard to start situation and noise
It would set it deliberately a little late at this point in time
The revving up at start can be the idle setting or the idle circuit
On my 80 there is an adjusting screw for idle that I would take all the way out
Are these starts with choke ?
I would consider if not already done take out the plugs and kick it around so oil gets distributed.
I would have oil in the cylinders doing this
Hoping piston pins get a little oil
I would do it and perhaps let it stand half a day and do it over .again
The same routine next day.
The priming kicks is perhaps not needed
Thinking out loud here I believe it needs oil at the top end rockers and so
Valve adjustment and a later ignition
But it is difficult to know ----If not getting better soon long shot ---->
??? Woodruff key for oilpump that one slipped out for me no 9 at assembly
But I noticed it. before cover on
Just putting this out here