not everything here is applicable to the qt, but this is "fred's guide," a good primer for moped repair:
http://www.mopedarmy.com/resources/articles/fredsguide/
here's a link for the owners manual for the qt50:
http://www.mopedriders.org/article_view.php?faq=2&fldAuto=41
also here's a link to the service manual for the qt50:
http://www.mopedriders.org/article_view.php?faq=2&fldAuto=45