Red/White wire for the CDI unit comes from starter switch with + polarity. This signal to the CDI unit occurs only when the engine is in starting phase. I think that makes some kind of ease for starting the engine.
That's what some of us figured, but have never found out for sure what happens with it. I intended to check it out but didn't get to it. It should be fairly simple, watch with a timing light during starts with the red/white connected/disconnected.
On a cold start, some added timing advance can help, but on a hot start less advance is desirable for easy starts.
As far as I know, you're the first to check advance between the two cylinders. Was it running poorly? Edit: I see now, "top speed 70". I would look at fuel delivery, ... slide diaphragms, carb vents, float height, etc.
Using a strobe, independent of ignition signal, would not be accurate. The light needs to 'see' when the spark occurs. That's why a timing light uses the coil wire to trigger the light. With the strobe, you're only seeing the timing mark when the strobe flashes, but not when the actual spark event occurs.