RE: Why does engine want to start backwards?
The setting of the low-speed needle (or that of the high-speed needle) does not directly affect this.
While the engine is being flip-started, it does not draw any fuel through the carburettor...
It only runs on that fuel that is already inside it; whether from priming, or from the last running seconds before it was shut down.
All shaft-valve two-stroke engines have a limited capability to run in the opposite direction, although in a very ineffective way...
If an engine does start backward, you will be able to advance the throttle to about 20-25% open, but no more...
If you're lucky, at that point the engine could 'kick-back' and begin running normally. Or it will just conk-out...
Over-priming is the main reason for this to happen.
I have seen cases where over-priming with forward-flipping, caused a kick-back so strong that the prop was jarred loose.
(Kick-back on back-flipping will only tighten the prop in place... Besides, this is how all my engines are started...).
With a single nut holding the prop, you would have no way of knowing, until the engine begins 'shrieking' in flight, after the prop flew off...