polyurethane is generally very hard, can sometimes be slow to dry depending on the type you get.
enamel is usually pretty decent, did you use enamel with a hardener or just straight enamel?
i'd get a hardener with it next time if you didnt this time.
where did you get the paint? if it was in spray cans from like pep boys it may not be the best paint.
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there are no bicycles in the valley, the only bicycle you find in the valley is the bicycle you ride down there.
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