PLO8 missed river oop

[frizzante]

Hi folks. This is a typical hand and I often got the problem how to play after rivercard.

PLO8 100

fullring Table.

A [img]/images/graemlins/diamond.gif[/img] 2 [img]/images/graemlins/diamond.gif[/img] 4 [img]/images/graemlins/club.gif[/img] K [img]/images/graemlins/spade.gif[/img]
I raised 4$ preflop in LP and got a button call.
Button is a typical loose player with not much agression and most of the time playing for low.

Flop: 7 [img]/images/graemlins/diamond.gif[/img] K [img]/images/graemlins/heart.gif[/img] J [img]/images/graemlins/club.gif[/img]

top pair might be good and I Pot. he calls.

Turn: 3 [img]/images/graemlins/spade.gif[/img] which give me nice outs.

I bet around 60% of the pot and he calls again (which I expected).

River: 9 [img]/images/graemlins/diamond.gif[/img]

Hero ?

Should I let it go always?
When i think I can bluff him, how much of the pot should i bet?