I know I no longer have an America but the Scrambler shares the 270° engine so I think this is still in the forums ballpark. I have a new vibration in my foot pegs ever since I've installed a new chain and sprocket kit. I haven't checked the carb sync since it was adjusted just weeks before the chain went on but it was really good then.
When I ordered the regular steel sprockets were out of stock so they upgraded me to these:
http://sprocketcenter.com/street-sprocke...bler-07-14.html
and I just wonder if the lightened 18 tooth front sprocket might not be dampening the vibration as much as the 19 tooth big lump that was on there before. I've checked the chain slack and it's right in the zone for the Scram. Any ideas?
The EK X-ring chain is really nice and beefy and way smoother in operation than the worn stock chain.

A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)