The vigourous shaking may also be simply because it's not tuned properly. From memory the OS manual is pretty good at explaining how to tune your engine.

If you follow the instructions you will be a able to tell when the needle is in the right area. If you start rich (a couple of turns) and slowly screw the needle in the RPM will rise and eventually drop. You want the needle set a little before the RPM drops. Don't go for peak RPM either you want it a little before this to keep the engine rich (and cool).

With the OS 46 you should be able to hear the RPM. You shouldn't need a tacho.