*grunch*
check-raise turn, lead the river. If "weak" means he won't bet the turn again as a bluff or with a rather weak holding, I'd b/c. You have 15 outs here for your draws and your J could even be good. I don't know if that lifts you up over 50% equity but the 4 makes a quite connected board so I think it is the right time to semi-bluff a weak player.