1717 muggy cog

I am having some cogging issues i think. Sometimes it cogs and others it rolls slow then hit with the throttle.

Setup
1717 heli
Mmm
6s 45-50c 5k tenergy pack(2 3s in series)
5.5mm bullets on batteries an 6.5 on motor
50/14 gearing pinion might be a 16 gotta double check
Any ideas