Damn! I'm now having exactly the same problem with the Saito 56 on my Legionnaire!

That leaves me grounded until I find a solution!
Allan, I'll check on the vibration thing. Our club Saito expert spend almost an hour looking everything over and couldn't find anything out of the ordinary and couldn't find a solution. Both he and others felt it could be a fuel delivery problem so I'll check the plumbing.