You really should get a manual. The basic concept of timing an engine is pretty much the same for all engines. Because your bike might have points, first those need to be cleaned (or replaced) and adjusted for gap. If your bike does not have points, you should not need to adjust the timing. Either way, to check the timing you'll need a timing light and find the timing marks (typically on the flywheel) and use the timing light to see if the timing is correct. You might need to move the points backing plate to get the timing correct.
Here are some links for a CX/GL manual.
http://motomanual.com//catalog/product_info.php?cPath=22_30&products_id=55&osCsid=cc42fb90854e870c11b4123cbfcb2b36
http://search.yahoo.com/search?p=Honda+CX+and+GL500%2F650+manual&fr=yfp-t-501&toggle=1&cop=mss&ei=UTF-8
