Check this thread, it may help.
""Some experimenting I did a while ago after getting my KK 2.1 board suggests that the "lazy motor" issue is mainly due to the variation in KK processor clock speed. The KK board does not use a crystal oscillator, but relies instead on the AVR processor's internal oscillator which has a pretty loose tolerance - a few percent, compared to around 0.01 percent for a crystal.
Mine runs about 2% too fast, which means that the CPU calculates a value of about 1540 microseconds for pulses that are really 1500 microseconds (that standard stick center point). So, the board thinks that you are giving up elevator and right aileron input, and tries to head in that direction (towards motor 4).
I need about 20 clicks of subtrim on DX6i/AR6210 to get the standard KK firmware flying level, so you could try yours with standard firmware and lots of subtrim and you'll probably find it works OK. If it works OK with the 1540 firmware then just stick with that.
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also
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The board starts off by sending esc throttle signal directly from rx with no gyro correction applied. When you reach a certain point on throttle, lets say 10%, the board starts applying gyro corrected throttle to esc. If you have a gyro reversed the quad will begin to lift because it is only controlled by tx but when point is reached where gyro kicks in it will flip all of a sudden on that axis. If you have I at zero there should be no windup so it is probably you need to reverse gyro for that axis. The 1540 firmware works just like original so roll pot to 0 turns on gyro reversing.
;---- Gyro direction reversing ----
;---- 1: Set roll gain pot to zero.
;---- 2: Turn on flight controller.
;---- 3: LED flashes 3 times.
;---- 4: Move the stick for the gyro you want to reverse.
;---- 5: LED will blink continually.
;---- 6: Turn off flight controller.
;---- 7: If there is more gyros to be reversed, goto step 2, else set roll gain pot back.
found in post #2578 and #2676:
http://www.rcgroups.com/forums/showthread.php?t=1458663&page=172#post22298692