Google Translater API v2 large texts 'POST' method

Question

I've got the following code:

$.ajax({
          url: "https://www.googleapis.com/language/translate/v2",
          type: "POST",
          data: { key: "<key>", source: FromLang, target: DestLang, q: Text },
          headers: { "X-HTTP-Method-Override": "GET" },
          dataType: 'jsonp',
          success: function (data) {
                var ReturnedTextalert = data.data.translations[0].translatedText;
                setEditor(ReturnedTextalert, LongLang, DestField);
            },
          error: function (data) {
                   alert('fail');
            }
          });   
    }

This code works fine for small texts, but I can't get it to work as a 'POST'. It keeps giving '414 Request-URI Too long'. The text i'm trying to translate is just 2120 characters. It should be able to translate <5K characters.

Can anyone tell me why the 'POST' method in combination with the 'GET' override (which is explained by Google) doesn't work?