The battery may be new but is it good? If the voltage is fluctuating when it is running I would think you might have an issue with your altenator.
I do got a Honda b75 from early 70ies without CDI ignition that gives me a serious headache.
Cant get the engifte to fire,
after drop down the gear box try to shift manually, while turning shifter turn the drive shaft also. still its hard to shift or not shifting at all to
you have only two wire coming out from the engine, one wire goes to starter motor (original wire black with white stripe) that is positive(+) other black
hope both the adjusting screws are clear for you but Europe models you cant adjust the pilot screw unless you break the stopper so just see whether you