None of these bikes come with shims, steel or brass. Someone had to have added them.
What are your air mixture screws set to now? I'd try adjusting them out about a half turn and see how she runs.
On the shims and out of curiosity, how thick were the brass ones? Personally, I would try to get the bike within good running conditions with no shims and work with the jets to start. The shims are more of a fine tune.
