Hi
Welcome aboard
Im pleased to meet you
You could try lightly sanding the balls and the holes on the linkages to remove any burrs or imperfections
Read the tips here they are for coax helis but ive found they work quite well for FPs as well
Ive used the tips there on all my helis and they all fly perfectly now
http://www.rchelicopterfun.com/toilet-bowl-effect.html
Hope this is of help
Take care
Yours Hank