This all just isn't making sense my friend. Indeed, the servos moving that way is not ok, and indicates some sort of a problem with the ignition system, though I can't say that is the only problem you have. That problem may indeed be only the spark plug cap not on tight. You have to push them on very hard. You should also be running a resistor plug just to be safe.

It sure seems odd that you had it running perfectly on the test stand, and now on the plane it won't. That tells you something right there.

I think it is time to offer a case of XXXX Gold to someone familiar with small engines, and hopefully in aircraft applications, to come spend a couple of hours with you sorting it......

Sorry, but we are trying from here the best we can,
AV8TOR