My Raptor 60 w/OS70 has a tail issue. First flight is fine for about 4-5 minutes then the tail sort of pulses when hovering. Until then the tail is rock solid. I have swapped gyros ( from a JR 500t to a 401 & back), swapped tail servos (both digital), & yes the gyros were set to high speed servos. The drive train has no visible issues & minimal slop. I am beginning to think that the engine is causing the problem. There seems to be a slight change in tone. Mixture is good (lots of power & cool rear case). Running Cool Power 30% heli. Could worn ball link balls be causing this?

It could be the ball links but the tail pulsing would be there from the start, try to lean the engine out some , it could be that the engine is to rich and that will case the tail to twich like you describe.

I agree, try leaning it out a little. You said that the engine backplate is cool to the touch? I would think that you are too rich.

No the engine is too lean, you have to richen it a little when the weather turns cold.....

Sorry I didn't mention this in your other post. There is a small chance that after a few minutes flight your battery is going down low enough to cause tail twitching. Try to check the voltage when this begins to happen. Also look for lose wires going to the rudder servo and gyro.

Finally figured it out. The ball link on the rudder servo was not far enough out.

Thanks for all of the help.