My 3900 will occasionally do wheelies. I noticed it happens more frequently when the water is cold because, I assume, the hose is stiffer. I also see it happen when there are pool inflatables in the pool while it runs (again because there is more drag from the hose).
I would thinks that slowing down the sweep (water restrictor) might decrease the wheelies, but it might also cause other issues. Pointing the rear jet more downward might also lessen this behavior. You might also check that the hose swivels are not stuck or difficult to turn.
I don't see it as a problem because it still cleans my pool. It eventually gets the debris it may have missed because of the wheelie so why worry?
