The silver control on the side wall is labelled 'Advance' and 'Retard' and presumably sets the ignition timing
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/43851301@N02">tony_duell</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/tony_duell/14503750073/">Renown cab</a>