This post should answer your question. See the correction I made in the post below it too. This goes through a calculation for playing 2 suited cards, but the issue is the same. You are not getting the right odds in limit hold'em to call a full bet with these, even if you include implied odds. You certainly never have the pot odds, since even if you won automatically when you flop a draw, you can never have 11-1 odds before the flop except in the small blind. You need both flush and straight possibilities.