If fuel is going through the carb into the plenum, then there has to be some compression pumping the fuel. The only way I can imagine that NO fuel would go from the plenum into the crankcase is if the reeds were completely shut somehow. As I said earlier, the volume of fuel going through the carb is so great at low rpm that you’ll get quit a bit of it dripping out the front of the carb. Seriously, on my X125t I get fuel dripping out the front even at 4000 rpm.
If you use starter fluid it should fire without choking.
I’m pretty much at a loss and suspect there is something misassembled on the motor, or your ignition system is for an X30 and the timing is so far off the motor won’t start. You might have to bite the bullet and take it to a kart shop where somebody can give it a hands-on look, as remote internet diagnosis isn’t working.