I have had a very, very, very ,very very strange experience with the electrical side of engine operation.
My second engine would only run with the blue wire connected to the black wire and the other two wires connected the same way.
The engine ran terribly bad; it made no power, hardly even was able to push the bike along without me pedaling.
I spent 2 days swapping over all the electrics (new magneto, new CDI, new throttle kill switch) and flipping over the magnet and relentlessly cleaning the carburettor and changing sparkplugs but it would still only run with blue wire connected to black wire.
In the end i took the bike down to the retailer where i bought the engine and the shop mechanic spent the next two hours swapping over all the (new) electrical parts for new parts that were sitting on the shelf and a whole lot of swearing and buggerising around (even taking the electrical parts of his bike that worked correctly and swapping them onto my engine) and trying everything, including flipping over the rotor magnet.
Same thing happened every time (only ran with blue wire connected to black wire) - strangely, the electrical system never showed any sign of weakness and always had a strong electrical spark.
In the end, the shop owner gave me a new engine, and upon assembly in the bike, it ran perfectly with blue wire connected to blue wire and black wire connected to black wire.
The only thing that was never changed over was the rotor magnet, but i refuse to believe, and so did the shop mechanic that a magnetised rotor magnet creating a strong spark could be faulty.
To this day, i have no idea as to what the heck was going on with that engine.
Fabian