I just picked up a cub recently with the Saito FG-20. I seem to have a similar problem on my engine. The engine will idle fine and run fine a above 7000, but nothing in between. I tried the base setting on low speed and the results are the same. Not sure how long the engine has been sitting. High speed on a 16 x 6 MS is 8500. Sound of the engine at idle and at high speed sounds smooth.