It's hard to diagnose this one. My bet is that your mixture is wrong. If the engine dies at or near midstick, which should be close to having the carb half open, then it is a good indicator that the mixture is wrong at mid range.

Since you don't mention anything else, like blade pitch range, or rotor head rpm, or even engine brand, it is very difficult to diganose based on your description of the facts.

And as a side note, there is no reason to post twice. [link]http://www.rcuniverse.com/forum/m_7418039/anchors_7418039/mpage_1/key_/anchor/tm.htm#7418039[/link]

Rafael