Likewise another guy from a club up country bought two FA100s. One shakes like hell, the other is smooth as silk. Both have been run in the same, use the same fuel and even swapping props makes no difference.
Go figure. Some shake, some don't -- and it's not always down to tuning.
I've probably said this before, but some Saito engines have been mounted with wrong timing on the camshaft. If there is something wrong with the timing, this will lead to heavy vibrations between 50-80% throttle. I had a "shaker". The vibrations were so heavy that it damaged the rear bearing. But I realigned the timing and the problem disappeared.