Make sure your throttle is opening all the way and you have about 5 degree's of pitch and 50 percent throttle at half stick.

Ensure that your atv's are even away from center that is, dont have 60 left and 90 right, make sure they are matched or very close.

Make sure that the throttle geometry is correct, that at half stick the pushrod is 90 degree's to both the servo arm and the throttle arm.

Make sure your top end pitch is no more than 10 degrees and bottom stick is 0 to -2 all in normal mode.