Not all wheels are built balanced, lower quality wheels may not be built to balance. One of the reason why wheel manufactures went with machining because they can balance the wheel while machining the sides of the rim. The old school method of pinning the wheels, still practiced today to some degree, put the seam and pins opposite of the valve stem which was suppose to add enough weight when the tire and tube were in place to balance wheel. And some added material to accomplish that. Torelli Triumph series puts a counter weight on the opposite side of the valve and painted it gold so you could see it was balanced.

If you re read my post I explained how to balance a wheel if your having issues. If it's a rim and not a tire that is out of balance 999 times out of 1000 it's due to the valve stem, thus putting a weight on the opposite side like a computer magnet will take care of it. And you may feel the front wheel being out of balance but it would be rare if ever you would feel the rear. If you flip the bike upside down and give the front wheel a gentle spin and let it come to a stop on it's own, the heavy part of the rim will settle to the bottom thus any weight needs to be added to the top, and moving the computer magnet to that top area should take care of it.

Most out of balance rims is not the rim, it's the tire. And that is simply a trial and error procedure, by simply moving the tire 1/8th of turn on the rim in any direction and see if the imbalance feeling goes away or lessens, if it gets worse move back where you were and go past that starting point an 1/8th a turn. If it lessons but is still there then move it another 1/8th a turn and retry. Obviously you have to deflate the tire and loosen the bead to get the tire to move on the rim.

Unbalance wheel is actually a rare occurrence.