Mana problems with molten strike

Hey,

i build a molten strike jugg this league and build him like in this video: https://www.youtube.com/watch?v=wXhkPbRAyQs

In the video he says that by act 3 to 4 you will have no more manaproblems due a a manaleach skill. I build exactly like in the video and i have to take my potions all the time.

What am i missing?

Regards