[Pokey]

I call this down; you're ahead more often than you think, and when you're behind you've usually got good outs to at least half the pot.

The most likely hand that beats you is Kx with x>4. If opponent has KT, KJ, KQ, or AK, you're dead, but AK and KQ are unlikely given that there was no preflop raise.

If opponent has K9, K8, or K6 you've got 3 outs to win and 6 outs to tie.
If opponent has K3 or K2, then HE's drawing to 3 outs to win and 6 outs to tie; the other 38 outs give you the win.
If opponent has a pocket pair, he's drawing nearly dead. (I assume AA would have raised preflop.)
If opponent has A7 or A5, he's drawing to five outs.

By the time you fold, there are 6.5 BBs in the pot. You're getting 7.5:2 odds for a showdown, and I think your pot equity is more than enough to warrant seeing it, even unimproved. Plus, if you do hit lucky you'll be able to get a nice juicy check-raise on the river.

I call the turn, call the river unimproved.