Quote Originally Posted by yorib
Assuming he bets the pot, you have a 33% chance of winning so you could bet up to.5 the (bet + pot) which in this case is up to a pot size bet. In this case you call as you also have implied odds. (i.e. You know your opponent will continue to make/call large bets if you hit your hand.)
This is only true if he isn't gonna bet the turn anymore.

Pot: $2, his bet $1.5. Here you have to call $1.5 into $5 or 30%.

And after you call, and you miss on the turn (you had 1/6 to 1/5 to hit depending on the draw) the pot is $5 and he bets another $3.5. Now again you have to call around 30% for your 1/6-1/5 to hit. Without implied odds, this is -EV play.