I have a m4 and everything seems to work with is except it never goes straight always heads off slightly one way or another. It also just stays in the deep end of the pool going back and forth over the same spots. sometimes when its going up the wall it will go sideways also. Not sure if this is just how they are or not since its my first one. I have tried the floats in every position and the same with the handles on each side moving them. still just stays in the deep end. Is there anything i can check or try to change with it? I changed out the climbing wheels thinking maybe that was a problem with is not climbing the walls that often either. Sometimes it sill just get up on the wall stop and go back down without going all the way up also. The pump works well. when it gets to a wall you can see if really put out some water trying to get up.