Yammy 9.9 2 strokes are simple
Pre 1995 OB's have a 4 petal reed block, these need to be replaces with a 15hp reed block (6 petal)
Post 1995 OB's already have a 6 petal reed block.
In this case you can either replace this with a 15hp reed block or simply open out the reed stops to 25mm gap between them.
Also check that the carb butterfly is opening fully to the horizontal position. Make sure the engine is in gear (not running! Obviously