When you give backwards input, does it go "less forward?" That is, does pulling the stick back have any effect at all? In other words, when the heli is stopped on the ground (no throttle), does moving the right stick around move both the servos and swashplate? If so, your swashplate may need to be leveled. Also, check to see that it hasn't separated apart. You don't say what happened between the time it "flew well," and now, or what happened to make you want to change servos. Check back with us and let us know, and we can be of further help. Neall