10hp Snow King Adjustment Screw

I just put a rebuild kit in my snowblower. Last season, it was loping up and down while ideling. So I bought a kit this year and it was doing it again. I readjusted mixture screw on the side and once I remove the screw driver off the screw, it spins right back in to seated. Then it starts loping. I back the screw out 1-1/2 turns and it runs smooth, remove the screw driver and spins back in.....This seems odd to me.



Any one with some suggestions?