it should fly on its own without flashing
But it does fly . . . just not well.
The stock ROM on the kk2 is known to be buggy, so you might be chasing a hardware setup issue, or you might be chasing a bug in the firmware. From your description, (get above a certian throttle level some point above hover, the tail cannot keep level) it's a pretty low chance it's a software setup issue -- unelss the throttle level is near WOT, the board should have plenty of play in the control loops to balance the motors.
Hardware:
- Where's your CG? Is it near the center of the motors? (for a tri with 3 matched motors it will be near 1/3 back from the the front motor's centerline to the tail) If the CG is off, it should still work at low-to-mid throttle, but as you near the top end, you'll have trouble with the motors maintaining balance in pitch. CG does matter.
- Have you de-vibed the airframe? Vibration isolation between the contorl board and the frame? Ballanced your props? Any vibrations from the motors/props increase DRAMATICALLY with throttle -- I've had airframes perfectly tuned close-in, then go completly bonkers (dropping a boom while yawing wildly) in fast forward flight. catch it and slow down . . . tame as a kitten. The difference? higher throttle. Balance your props (I do them all at once, shortly after a new box of props arrives -- it's a pain but it will make a difference at high throttle), balance your motors, isolate your control board.
Software:
- Adjusting your I gain in pitch upward might help, assuming it doesn't go so high as to induce osscilations of it's own, but I doubt it will solve your problem. I will help reduce *drift* in angle, and what you're describing ain't drift.
- REFLASH. The stock ROMs stink. They're buggy, and they don't take full advanatage of the hardware to give you the best flight envelope. It's enough to test and ensure everything is functional -- mission accomplished: if you can hover, everything works -- but it won't work well under the stock ROM. The modded ROMs avaialble are a great improvement over what comes loaded. Even if one of the hardware fixes sorts this out, it's really worth your time to reflash it anyways.