Joyetech Aio D16

Hi to all

Iam from Portugal, sorry if my English is not accurate.

I'm new at vaping, I purchased here in Portugal one "Joyetech Aio D16" for 29$.

I used a few times and followed the instructions, I put a few drops of e-juice in the cotton of the coil, in atomizer head.
But sometimes I get a burnt taste, and also a few drops of juice spitting off the mouthpiece to my lips, why?

I adjusted the air flow rotatin 90º the joyetech AIO head...

I have another question : How long will last the cotton in the coil head? A few weeks of months?
I must replace the atomizer head (I don't know how to open and replace cotton in the coil, and will not try it), after a few time?

thanks