ajax is not completing the request

I am using ajax, php and a html form.

Ajax function:

$(document).ready(function(){
    $('#set_like').submit(function (e) {
        e.preventDefault();
        $.ajax({
           type: 'post',
           url: '/noutati/articol',
           data: $(this).serialize(),
           success: function () {
              alert('Succes!');
           }
        });
        e.preventDefault();
   });
});

HTML:

<form id="set_like" enctype="multipart/form-data" action="<?php echo base_url();?>noutati/articol" method="post">   
<input type="submit" name="submit-like-up" data-id="<?php echo($li_position); ?>" class="like-up" value="submit_up" /> <span class="counter-like-up<?php echo($li_position); ?>"><?php echo($comment->like_up); ?></span> 
<input type="submit" name="submit-like-down" data-id="<?php echo($li_position); ?>" class="like-down" value="submit_down" /> <span class="counter-like-down<?php echo($li_position); ?>"><?php echo($comment->like_down); ?></span>
</form>

It shows the Succes! alert, but is not completing the PHP request. Any ideas why?