I mount mine then put the tire on the balancer before I put any air in them. I leave the tube nut a couple turns loose. If the balance is real bad I spin the tire on the rim until I find the best balance spot. Once I find spot, I turn the tire just a little more, then back to the sweet spot so the valve stem sticks out straight.
When I air them up I leave the core out. Fill the tube with air until bead seats, then let all the air out so the inner-tube can relax and find its comfertable position, then put the core in, fill it again and set the pressure.
All my dirt bike days cause me to leave the valve stem nut several turns loose so I can see if the tire is moving on the rim (valve stem will no longer be straight). if you tighten the nut and the tire spins on the rim, you will rip the valve stem out of the tube (and you end up walking).
2000 KTM LC4 640 E