Value betting the one-card flush

[Aaron W.]

The game is loose passive. How big must x be to value bet the river?

Would you take a stab on the flop or turn to try to pick up the pot?

Paradise Poker 1/2 Hold'em (5 handed) FTR converter on zerodivide.cx

Preflop: Hero is BB with 3[img]/images/graemlins/club.gif[/img], x[img]/images/graemlins/heart.gif[/img]. MP posts a blind of $1.
<font color="#666666">1 fold</font>, MP (poster) checks, Button calls, SB completes, Hero checks.

Flop: (4 SB) 5[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero checks, MP checks, Button checks.

Turn: (2 BB) 2[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero checks, MP checks, Button checks.

River: (2 BB) J[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero ...