I guess I've been rather preoccupied with the D!, Green Gremlin, and have neglected my Little Willie. Today, however, with the sun shining down - as if in approval - I began checking the D7 over, starting with the spark plug.
To my surprise, I found the source of the problem quite easily - no not the plug! - it was the points! They'd actually opened up, not closed, resulting in a weak spark which was stifled every time I opened the throttle. The D7 would start OK, just a couple of kicks, but would not rev. But now it does! We've been out for a test ride and she went perfectly - and I noticed all the looks of admiration had returned again! Long live Little Willie!