WIERD! Need of help

Okei.
Heres my problem, I've been "flying" a piccolo fun with the piccobaord plus and the custom engine on, when I decided to switch to Lithium batteries for the exrte "flight" time when the heli all of a sudden got a fear for heights. When I push the throttle all the way to the top for maximum lift, it only hovers about 12 invehs above the grounds and dosn't seem willing to go any further. My question is as follows: Has the engine gone caput? I use a 2 cell 1000Mah lithium battery, so I thought that maybe the battery doesn't deliver enough voltage to the engine but the same thing happened with the original battery before I changed (that was partially the reason for changing to lithium batteries). How could I find out whats wrong?

P.S. I'm ordering the 310L tuning motor, hoping that will help. Oh, and by the way, just ask if there was any other info that I left out that is relavent to discover the problem.

In advanced, Thanx

Lesstthebest