Here is the official 1978 Honda NC50 express owner's manual (UK Model)! I can't believe it has taken me this long to find it. This is different from the Honda express shop manual that can be found on this website as well. Here is a few small excerpts from the document:
This booklet is your guide to the basic operation and maintenance of your new motorcycle.PRE-RIDING INSPECTION:
Please take the time to read the Owner's Manual carefully. As with any fine machine, proper care and maintenance are essential for trouble-free operation and optimum performance.
Your authorized Honda dealer will be glad to provide further information or assistance and is fully equipped to handle your future service needs.
Thank you for selecting a Honda. We wish you many miles of continued riding pleasure in the years ahead.
At the start of each riding day, perform a general inspection to be certain the motorcycle is in good, safe operating condition.
Gasoline Level - Check gasoline level and fill tank if low.
Capacity: 2 liters (0.53 U.S. gal., 0.44 Imp. gal.)
* Use low-lead or regular gasoline with a Research Octane number of 91 or higher, or a Pump Octane number of 86 or higher.
For Australia and New Zealand models; Use unleaded gasoline only. The use of leaded gasoline will cause spark plug fouling.