The manual calls for NGK B8ES. I ordered one from Amazon and the one I received is a resistor plug, BR8ES. Will this plug work on a 1975 DT175?

If it runs she'll be good, but i guess the plug has about a 5k ohms resister & the same with the plug cap so might be a lot to ask for a magneto ignition. No harm done trying it i guess. Also, don't take too much out of what i say as i just tend to "try it & see".

If it doesn't run well , you could change out plug cap for non resistor type , which should
put you in the ballpark of resistor cap and non resistor plug .
If it runs fine , I wouldn't worry .

NGK has been phasing out the non-resistor plugs. You can still get a non-resistor Autolite which is what I've been using for many years.

Added resistance will reduce available spark energy. The thing about spark energy is you only just need "enough" for the conditions in the combustion chamber.

Gap it properly and it will almost certainly run just fine.

The downside is with less available spark energy misfires and plug fouling will be a little bit more likely. Using a non-resistor cap as suggested is a perfect course of action if you stick with resistor plugs.

("Resistor" is what the "R" stands for in BR8ES in NGK-speak )

I took Mark's advice and bought some Autolite 4054s and my CT-1 IS running better. With the resistor NGK plug it would occasionally stall when sitting at stop lights. Has not happened with the Autolite, and it seems to run stronger overall as well.

I started running the Autolite 4054 that Mark T suggested in my DT2, runs great!  So I started looking for an Autolite for the B9ES to put in my DT400 and came up found the chart in the link below if anyone is interested.

NGK spark plug cross reference chart

You can get the NGK still from here

www.chapmoto.com/ngk-standard-b8es-spark-plug.html

I FINALLY got my 5 packs of Autolites today! They said they were in stock, but it took well over a month to get them. No worries. I still had some NGKs on the shelf.

I got a box of ten from them a few weeks ago (Chapmoto) and I just hope they are not cursed.