I have a .51 Italian, but the spraybar was modified. The flat milled spraybar from the .90 woke the .51 up quite a bit so I shaved the round spraybar down from the .51 carb... I'll have to pull my 45 apart and look at the piston - I don't recall it being all that bulky/heavy...

If you're used to the small guys and run big ones, they do seem to shake more... Ever run a big Jett? If your tank isn't bubble-free, you have essentially whipped cream in the tank running at full power. My biggest Jett is a .56 and even with a perfect balance on the prop, it'll still shake things up and I'm only running that one at 16,500 since it's still pretty new and a bit high strung still.