Start by making sure that the grub screw(shift point adjustment screw)is still there.Mine shifted perfect out of the box.Mine also suddenly stopped shifting.I couldnt figure it out.After I took it apart,the screw spring and ball were completly gone,mind you I had never made any adjustments.I ts hard to tell if it is still there with your allen wrench.Youre gonna have to use a flashlight or take it apart to tell.you will have to threadlock that grub screw after you get it set,or else it will come out every time.If you made any shiftpoint adjustment and didnt threadlock the screw,then theres a very good chance that the screw,ball and spring are gone.I contacted cen about this,and they send me enough screw,ball and springs to last a long,long time(free of charge).Check that out and get back to me.We will get that magnum running right