[speeder]

Originally Posted by Rot 911

As the owner of several airheads, presently a 1965 R60/2, the higher you go up in displacement, the more vibration you’re going to feel. The 750s, in my opinion, are the smoothest of all the airheads. If you feel better spending $800 on those rods, go ahead, But I don’t think you’re going to notice any reduction in vibration. And it’s not like they vibrate a lot to start with. As for synchronizing carburetors, I have found the Carbtune, to be the easiest synchronizer to use. Comes out of Ireland, but they ship quickly. https://www.carbtune.com/

This right here. ^^^

I think that the smoothest old airhead was the R60/5. My neighbor got a new one in about 1969 and was showing off by balancing a coin on fuel cap while it was idling. That memory sticks with me.