Just my 2 cents worth but with a clicking noise when rotating by hand could mean a bad 1 way bearing or loose in the clutch and or a bad rod to piston connection or a bad bearing in motor allowing too much for and aft movment. Make sure you have the proper plug in . A #8os is what I like. Make sure your plug is not touching the piston. Pull the motor, check it out. if it is clicking by hand out of the heli then I would send it to manuf. Also check everything connected to the motor at the heli. Make sure you don't have a tail belt twisted as it will click and have a ruff sound and feel. yes rich will cause backward running, a rich low end mix will have a rattling sound at idle and mid range and you will swear the motor is comimg apart. Check that noise out for sure.

JIM