Well, here's a link, a really good one that explains it better than I can: www.foxvalleykart.com/timing1.html

In your case, I would use a timing light to make a mark on the case (and flywheel) to indicate the present timing. You could then experiment from there. If you want to know the timing in degrees, just use a degree wheel to check what degrees your mark actually indicates BTDC.

Good luck,
AV8TOR