I maidened a little no-brand Chinese .40-size Ultimate ARF today (exact copy of The World Models Ultimate). I used a new Super Tigre .40 ringed for power. I was having a hell of a time getting it to run right... it was unresponsive to the needle at times due to what seemed to be fuel foaming. I was getting some nasty vibration with harmonics shaking various parts of the airplane at various RPMS. =:-0
I took off the prop and checked the balance... fine. Then I took off the cowl and checked the engine mounts, the engine mount bolts, etc... fine.
When I got home, I decided the put the spinner on my magnetic prop balancer. It was way out of balance. Even after drilling six 1/8" holes near the rim of the backplate on the heavy side, it still wouldn't come close to balancing.
The spinner was one of the very nice-looking polished aluminum types that I bought from either Maxx Products or Cermark. They are very inexpensive and look great. I took it off and replaced it with a high-quality (and high-priced) model and everything is running smoothly now.
I guess I'll be avoiding the budget spinners in the future....
Good flying, desmobob