Have you run ESC calibration? Take a look at this: http://code.google.com/p/arducopter/wiki/AC2_ESC
You may need to do the manual calibration of your ESCs. Also, just double check the wiring... I have sworn I had everything connected properly only to find a problem.
Well I hope you get it figured out... sometimes walking away and coming back helps in and of itself. Good luck!
If they all are calibrated properly (you can check by attaching ESC wires to the receiver throttle channel and check that the throttle range is the same for all of them) the other possibility is that your copter is not level - or it thinks so. Does it show horizon as level in Mission Planner? Try recalibrating autolevel and try again.
And btw the ESC calibration never worked for me on hexa, only 4 motors spun up. So maybe you missed two of them this way.
It sounds like you should be able to get lift at 70% throttle. If it is possible hold the hexa and see if you are getting any lift at all. Maybe your props are backwards, or your motors are still connected incorrectly.
My flyduspider is 1.5kg with battery, 1.7kg with gopro, and still lifts up at ~60% throttle. Ideally it should lift with 50%. There is no answer to how heavy it should be, I had larger motors in there that added +300g themselves, but there is usually a typical weight for a particular frame.
However at 1.9kg it shoul lift just fine with 10" props. Is your battery hot? Are you using 3S battery with that motors?
Yes, I am using a 3S battery and it isn't getting hot.
Assuming the motors aren't cutting it, I am using eCalc to find the best motor for my copter and I've narrowed it down to the following:
The NTM is not preferred because of the price and the 6 new ESCs I'd have to get. With those I'm not getting a flight time of more than 6 minutes.
What are you getting for flight times with your copter? Also, what battery are you using? Could you post specs so I can compare?