Is it a 6v or 12v engine?

How can you tell the difference between a 6v and 12v engine?
Does the engine number help or are there any obvious electrical plugs that differentiate this?

Thanks

Blue

if it is a 12 volt it will have a cdi

Pickup instead of points on the stator.
Different brand / kind of flywheel.
Different engine number.
Different battery voltage etc.

Be aware, a 6v CDI engine also exists.
As well as an 6v ignition with 12v output.

Thanks guy's not as easy as I thought.
I have a spare bike that has no engine, I want to put a 12v in it so was on the hunt for a 2nd hand engine to fit.
Maybe I'm better of buying a new engine, maybe a Lifan 125 like this?
http://www.ooracing.com/store/index.php ... uctId=1742
Are these any good or is there a better alternative for the same price?

Thanks,

Well, you basicly have 3 options:
- big bore Chinese engines.
These are very cheap, can be decent, can be bad. All have a pretty bad cc VS bhp ratio. All are pretty ugly imo, differ a lot from the original look.
The Jingcheng DX90 or pretty fast (the older version, not the new), can be converted back to 6v system. Look like an original engine, especially if you put Honda covers on them.
- New Honda Nice / Wave engine.
Very reliable and perfect cruise performance. Very expensive, and... again in my opinion... very ugly.
- Tuned Honda NT engine.
These engines are new, fresh, often low mileage and easy tuneable. If you keep these stock, they are bullet proof.
Stock they sell ate the same price as the Chinese engines, but they are slower as a 50cc or 72cc. Tuning parts can be pretty expensive.
Best looking engines.
(Have one for sale, superb deal especially if you want to built one yourself)

I'm reading this thread and I didn't realise that I might be in a bit of trouble.When I bought my st70 I took the opportunity to buy a reconditioned engine at the same time because the original engine was in pretty bad shape and will take lots of time and money to reco.The original bike and engine are definitely 6v as they date from 1969 and the engine number is st70 E122757.The new engine which I've almost installed has the number ct70 151978.I've noted what you're saying about the differences between 6v and 12v,but can you tell an electronics novice what CDI is?? and any other things I should look for. I don't know if it's relevant, but the electrical connection coming from the new engine fits straight into the connection of the old loom.Thanks.

Thanks Waynus, more research needed I think.
I want a 12v engine', Ideally honda or something the looks the same, don't want it to be slow but I'm not looking to break the national speed limit.
Never heard of the Honda Nt, what did it come out of? Is it 12v, what cc is it?

Cheers

Blue

Honda NT (new type) is 12v.
Available in 50cc and 70cc, easily tuneable tot 85, 88 or 106cc (SCUT).
Can be XR50/70 engines, CRF, NT50/70, Z50R,...

Roundwound, CT is the American version of the ST.
Can be either 6v or 12v.
A CDI is an electronic device which provide the correct pulse for ignition.
(Capacitor discharge ignition)

Does anyone know if a Honda C90 12v with an electric start fit in an ST70?

Some of the, not all.
You have these with 2 different kinds of semi clutch cases.
The fat harry version won't fit your frame, as it is too wide.