How do I return a 401 authentication error to a RestSharp client?

Question

In my Mvc Api controller, if the user cannot be authenticated I throw an HttpException 401. However, the RestSharp client seems to translate this into a Http 500 status code.

I want to be able to throw HttpExceptions from my Mvc controller, and have the RestSharp client preserve the original error in its StatusCode property.

Also, I notice if the server is not up, when the RestSharp client makes a request, the reponse has a status code of 0, and a response code of Error. Should the RestSharp not return a 404 http error code instead?

What I really need is a bit of documentation on how RestSharp works with HttpCodes.

Updated with code in my api controller:

throw new HttpException((int)HttpStatusCode.Unauthorized, AuthenticationError);