I kinda had a similar problem when I went to brushless. Took me FOREVER to figure out what it was. The main shaft retaining collar must be set for no play. My CPP came out of the box with play, so I thought this was normal. I guess with the stock motor I didn't notice it. But with the brushless w/ 9t it seems to have at least twice the headspeed, so i think my problem then showed itself.