Pass A String To A Web Service Using JQuery / JSON / AJAX?

As it is now I create a JavaScript object and then stringify it, put it in a hidden textbox and my code behind can read this string. I then use JSON.NET to parse the string which works fine. I now try to use ajax to post it to my web service but have some issues with how to send the string. I have tried many ways but gets the common errors like

Invalid JSON primitive: myString.

So I checked this out [URL] and it works with hard coded values but I want to use a variable.

JavaScsript to create the object:

for (var i = 0; i < results.rows.length; i++) {
var row = results.rows.item(i);
var customer = new Object();
customer.id = row['id']
customer.name = row['name']
var customerString = JSON.stringify(customer);
$.ajax({
type: "POST",
url: "synchronise.asmx/synchroniseCustomers",
data: "synchroniseCustomers: " + customerString,
contentType: "application/json; charset=utf-8",
dataType: "json",
error: function (xhr, status) {
alert("An error occurred: " + status);
},
success: function (msg) {
alert("success");
}
});
}

WebMethod:

public void synchroniseCustomers(string customerString)
{
JObject o = JObject.Parse(customerString);
string id = (string)o["id"];
string name = (string)o["name"];

If I use data: '{ FirstName: "Dave", LastName: "Ward" }'

in the example above it works but I wish to pass on a string instead.