I have the WB230 and I've had trouble getting a good balance before also.
Almost always it is because I don't have the wheel mounted on the balancer well - in other words it was operator error, not machine error. Especially on heavy wheels I've got to make sure the wheel centers on the cone and the cone spring is keeping it centered. You've got to hold some of the weight of the wheel as you tighten the nut.
After several frustrating bouts with it, I finally got the hang of it and I can balance wheels to where you can't feel a hint of vibration at all. And I always take the time to do the 90 degree turn and make sure they stay in balance. For awhile I would put it down on fine and get the wheels down to all zeros, but I find that I can't feel that last .1 ounce.
I really enjoy driving with well balanced wheels.
FYI - I looked for about a year for a motorcycle kit for my balancer and couldn't find a used one anywhere. Snap-on - or the company that handles parts for older snap-on stuff could get me one for something like $600 - which was way more than it was worth. I decided to make my own. It took about three hours work, and a bit of tweaking, but I got it done and it works great. The trick is doing everything centers on a lathe, and making sure the part that fits into the bore is a really good fit.