Could it be an issue with weight distribution? The back is quite heavy since it has the battery.

NO, my quad is not uniform in weight, even angles are not exactly 90 degree (my custom frame)

still I can fly with out any problem.

which is your KK firmware version?

Version 1.9S1 came pre loaded. My update tool is still shipping.

that is new firmware - but in my case, one update solved all my problems
but you can still fly the quad by compensating it's flipping through manual stick movements, it's little tricky, but it can be done. I mean, if quad flips backward, give a little forward pitch wile take off .
But if there is unwanted movement, once the quad is in air, immediately land it.

I am barely able to get it off the ground. it is really unstable and drifts a lot when I try to hover. If I increase throttle it flips. What do i do? As of now, I am charging the LiPo. I will try again later.

these were the same symptoms I had, broke 3 props, by flying withese conditions - but a firmware burning magically solved all my problems, nothing else !! . Now It won't drift even if I take hands from controls !!

watch my flight video - in HD .
www.youtube.com/watch?feature=player_detailpage&v=6FSuqgml5hI

you can see, the behavior of quad with perfect PI tuning in the end of video

Guess I will try one last time and then wait for my firmware update tool. Reflashing the firmware might help.

No wonder I was having so much trouble. My firmware is 1.9S1 when the latest is 1.19S1 (Btw, it looks like the .xx part follows an order like 1.10S1 after 1.9S1). I am 9 versions behind! The gyro may also be reversed since when I tilt the quad forward, the bubble moves back slightly. I am not going to risk flying until my programmer arrives.

No, that is normal .

Oh ok. I thought it might be a problem. Anyway it appears that the only issue now is old firmware. My PDB is also pretty ugly so I am replacing it with this harness: http://www.quadkopters.com/product/multirotor-accessories/xt60-to-4-x-3-5mm-bullet-power-breakout-cable/. If I can get this quad to fly I have a lot of upgrades planned  such as using an APM board with GPS.

KK2.0 itself performs best for me - APM is advanced, still you will love KK2 after correct tuning- !!

P.S when you upgrade count me in line to buy your old KK  !!

You really are an opportunist  . Arducopter was the first thing I read about in the field of multirotors and I always wanted one after watching this hilarious episode of Flite Test Anyway, the upgrade is at least a few months away. i need to get this quad in the air first and learn how to fly and plus the kk will be a great backup board even with an APM.

you caught me

Haha   . It's time to put my quad away (at least for one or two days) 

you can't do that, you will understand gradually

Success (a minor one)! Since I am too impatient to wait for the USBasp tool, I decided to flash my kk with the newest firmware using my Arduino Uno an an ISP. I followed the instructions here: http://blog.oscarliang.net/flash-kk20-16-firmware-upgrade-arduino/. SInce I have a Mac, I needed to make a few adjustments to the procedure. I will start a new thread on this topic.

Oscar liang's blog is a best place to start learning multirotors, he has so many tutorials ther, I learned a lot from it.
When using arduino as ISP, make sure you correctly connect vcc and ground to ISP port in KK board, if you are unsure by any means, just connect vcc and ground to ESC or receiver terminals, but don't worry oscar have done a nice job there, by marking pins of KK ISP header - You can only use terminal to flash using Arduino as ISP, KKflashtool can't be used I don't know how it is done in mac.

I modified the procedure from my (average) knowledge of Mac. It is really not that difficult if you have been using Mac for a while (as I have). Check my new post here: http://www.rcindia.org/multirotors/updating-kk-firmware-with-an-arduino-(on-a-mac)/

so, have you test how new f/w performs ?
sorry- saw your reply on other thread - well no flying topic on other thread, ok

Good idea. Let's avoid confusing the other thread. A firmware update solved all my problems and I was finally able to get my quad in the air. What an amazing feeling! I had several rough landings and managed flight times of only 15-30 seconds (lack of space). I will go to one of the empty sites in my layout tomorrow and practise. I will also have to do some tuning. Does anyone know about any good simulator that has a quad (preferably for a Mac but Windows suggestion are fine too.)? I also found a good sim on the iOS app store and will try it out.

well why you need a sim ? - you are gonna fly a heli or what
flying a quadcopter is easy dude (once it is correctly set up ) .
just go to a open space without trees, and practice hovering the quad, don't get it to more than 3- 5 mts high, and also avoid testing the range of your radio .
you can use those yellow smiley balls fitted to your landing skids, for dampening the effect of rude landings while practicing.

Wish you safe landing

You have lots of experience, so I will listen to you and not get a sim yet  . I will practise tomorrow. Going to try and pick up some of those smiley balls. Should I hot glue the sponge balls to the landing skids? I am definitely not going to let the quad get more than 30 feet away from me. I just need to resist the urge to cut the throttle too much

well I can't agree with that - I have flying experience of only 3 days , and it is 4 charge cycles of a 3S LiPo .
But what I said is from experience gained in these mere 3 days !!

you can attach smiley balls to landing skid by any means - I didn't used it and learned it's need while practising -

From all your help, I thought you have more experience. You definitely have excellent knowledge of multirotors. Speaking of your charge cycles, did you get a charger? Which one? I saw that you hadn't received a charger from another member even after a month. I am using a clone of the IMAX B6 and I am happy with it's capabilities. Which LiPo are you using?