Imho, if you have anything in writing regarding the acceptance of the deal, they are obligated to fulfill the order unless there are some rather major extenuating circumstances. However, with the bike already in hand, it's not like they can say there was a price increase in between signing the deal and delivery, or a delivery delay to muddy the situation. Just merely saying the dealer changed his mind and is keeping it, is NOT OK, and is breach of contract for which you have a right to recover your losses.
Granted, this might cost you more than you will get out of pressing the issue, but it's something you should definitely bring up with MOCO and the area attorney general. Might even want to make a BBB complaint. I would however try to connect with the owner and let him know what you are contemplating and give him a chance to correct the situation first.
Imho, they got a better offer and are not keeping the bike. That makes this all that much more inappropriate.