what are you looking for out of the "visit" is the better question. there are no japanese manufacturers dealerships in the city anymore and if youre into euro bikes scuderia and monroe. if youre into the harley stuff check out california choppers. if into scooters look for the sf scooter center as they have a little "museum" of scooters as well. theres sfmoto if youre looking for off brand bikes and used bikes too. theres also mr scooter, tokyo moto , and motojava as well for small shops.
for the most part all these shops are about 10-15 block radius of each other as well so it makes it a bit easier.
scuderia west, dianese, munroe motors, bmw mc of sf, sf moto, moto java..i even recommend dropping by johnson leathers...mission motorcycles in daly city...cycle gear...
see the old building that once was the home of golden gate cycles ...