VS 2010 Chinese Encoding Causing Invalid Xml?

I am creating xml files that contain chinese posts and it seemed to be working but I started getting an error:This page contains the following errors:error on line 4165 at column 25: Input is not proper UTF-8, indicate encoding !Bytes: 0x0B 0xC3 0xA5 0xC2

Below is a rendering of the page up to the first error.When trying to open some of the resulting files.The line it references contains chinese characters and the error occurs only for some posts and my guess is that the text has some encoding issues.

Public Shared xwriter As XmlTextWriter = New XmlTextWriter(xmlfile, Encoding.UTF8)

I make sure the xmltextwriter is properly declared and set the encoding and from what I understand is that vb.net encodes everything in utf-16. My code works well with streams I get from another source that sometime contains chinese characters and it never invalidates the xml. I tried cleaning the text using the following functions and the xml is now valid but when viewing the xml in the browser the characters are not chinese but junk.

Private Shared Sub replaceIllegalXMLChars(ByRef tempstring As String)
'remove any hexdecimal characters like  and �
tempstring = Regex.Replace(tempstring, "&#x([0-9A-F]{1}[0-9A-F]{0,1});", " ")

[code]....

so if I need to fix my data, my question is how can I detect what encoding is used for a specific text and how do I convert it into utf8 format that can be viewed in an xml file and make the file valid.

EDIT: I messed around with converting from one type to another, first ASCII to UTF8, then Unicode to UTF-8. did not work. The only time the xml is valid is when characters display as such:

油价，老百姓心�*永远的痛！ � 民生、控物价一边说，油价一边涨，国家真得是为了老百姓的民生� �？