Quoted from FatPanda:
Finally got around to installing the chopper mod. Spent way more time on it than I thought I would lol. Thanks Mr_Tantrum for the tutorial! My blades aren't spinning as well as they use to and I made sure to install the washer/bearing/washer stack correctly. My initial thought is the the bottom washer is binding on the helicopter itself. Does the whole stack need to spin freely or just the bearing? Any other thoughts?
I suspect your hole at the top is not large enough and is causing friction/drag on the bearing assembly. In all the copters I have done, it required a hole larger than yours in order for the blades to spin freely.