I had been flying a PA-28 Archer III for quite a few months before I sat down to properly read through the POH. Something stood out to me about the starting procedure (emphasis mine)
Open the throttle lever approximately 1/4 inch. Turn ON the battery master switch, alternator switch, left magneto switch and the electric fuel pump.
Move the mixture control to full RICH, verify the propeller area is clear and engage the starter. When the engine fires, release the starter switch, and move the throttle to the desired setting. Turn ON the right magneto switch. Check the oil pressure for a positive indication.
Having previously flown aircraft where a key operates the starter, and that key has to travel past left, then right magneto to the start position I was starting with both Mags in the ON position (For those unaware, the Archer III varies in that the left & right magneto are operated by a rocker switch).
The obvious answer to the question of "Why start the engine with only 1 magneto live?" is "Because that is what the POH says to do!" - I am nonetheless interested in the electrical or mechanical reason why? Or perhaps there is some safety aspect at work?
Does anyone know the details?