Now thats worrying.I can explain the setting of the LS needle at the factory but the timing gear thats another. My 100 was smooth running before I traded it in for the 125.You know, my 82 has the same characteristics as yours,the vibration peaks at 80%.Looks like I'll have to check the timing then to see if they set it right at the factory.I'll check the other engines still in the box if any are out too.
Before i proceed though , did you set the timing different from the recommended setting or was the factory setting different from the recommended setting?
I retarded the timing by one tooth on the wheel. After that, the operation became smooth like silk. Power was still good. However, according to the manual it's not supposed to be like this. There is no problem with piston / valve clearance. Just check this before you turn it over to be on the safe side.
The reason for this shaking between 50-80% could be that the timing is set in a way that some hot combustion gases are not expelled though the exhaust cylcle. This will give detonation due to higher temp in the cylinder during the compression stroke. Higher temp will give predetonation until the RPM gets so high that combustion delay will cause the peak pressure to come to correct position. During lower RPM, the then during compression will decrease, hence no detonation.
Bigger prop and the problem will increase.