they move together but will engage at different times... check to make sure you are turning the correct set screw for 2nd gear... it is the angled one not the straight one.. start in and work out... not the other way around... I don't think the tires are the problem.. I believe its the 2nd gear setting or the engine isn't tuned for speed... When you said you felt the screw was loose and was starting tome out, I think you may be working with the wrong screws... let me know...