HELP! I need new spark plugs for my 1971 HT-1B restoration. I have reviewed the spark plug reference in the Tech library (didn't find the HT-1B on the list), looked thru the owners, factory service and technical manuals and searched online, but every resource suggests a different NGK plug. So, I'm here to ask the experts. After all, no one knows better than the members here who own an HT-1. What NGK plugs are designed and recommended for the HT-1B? I've seen B8HS, B8HCS, BR8HS, B7HZS, among a couple others. Any guidance is appreciated. Thanks!

Going by Partzilla it shows B8H which i'd call B8HS. They're in a pretty low state of tune so around town i'd just run a B7HS but if ya going balls out on the highway & the motor is well cleaned out then i'd run a B9HS. I know that's confusing but spark plugs are confusing & only you know how hard you're going to push it. Miss my little HT1. No15 below.
www.partzilla.com/catalog/yamaha/motorcycle/1970/ht1/electrical

RT325, thanks for your recommendation. The bike will be ridden around my subdivision and not ridden too very hard, so perhaps the B8HS (or BR8HS) would suffice. I figure that plug might be an all-around, "middle of the road" for normal riding. Can you (or anyone here) tell me what Yamaha recommended back in the day?

Tech library has a PDF of the owners manual. Lots of details and this paragraph lists stock number and some options for different conditions.

Some of those original numbers are obsolete and superseded

Normal riding would be B8HS

Low speed riding B7HS

High speed, hard riding/racing B9HS

Thank you all for the help!