you either have a massive air leak somewhere that is leaning the mix out so much it is "dieseling" and continue to run even with no spark. or your carb slide is hanging up in the throat.
for an air leak, my guess would be the main engine seals, either behind the flywheel or behind the primary dve gear under the clutch cover. if the bike is blowing heaps of smoke, its the primary dve side seal as it will also suck oil in.
pull the flywheel cover off and see if there is oily gunk in there just to check.
can you see into the carby throat to check the slide is hitting rock bottom every time?
the fact that you can idle it then it screams is a bit weird but reed valve gaskets can suck and blow as can the carb rubber boot to reed block. if it has a split in it. it can seal nicely till you hit the throttle and the vacuum opens up the crack letting a heap of air in.
it has to be an air leak. I just don't think you've found it yet.
But wait!! there's more .....
also check the fuel tap is letting enough fuel out...... I wonder if the jets are blocked enough to give that running out of fuel rev out....
may pay to undo the big nut on the bottom of the carb bowl and see if fuel runs out everywhere (not on the lawn!). take it off carefully and look inside it to see if its clean or cruddy as its like a trap for water and dirt.
Turn the fuel tap on and make sure a good trickle of fuel is pouring out everywhere. that will eliminate stuck needle or floats.
have a look at the main jet (little brass thing sticking out the bottom of the bowl (92063) and see if its clean brass looking or covered in fungussy stuff.
if its cruddy looking and there is junk in the bottom of the big nut, you need to pull the carb off and get it cleaned. it could be blocking the fuel which will make it like an air leak.
have a look at all that!
