Electronic ignition, start on one or both ignitions?

[Battson]

I am used to flying with mags where normally only the left one is used to start the engine. Is there any reason why I shouldn't wire my electronic ignition to start with both ignitions engaged?

[jaredyates]

Pmag documentation says use both.

[Battson]

Good enough for me, thanks!

[BTAZ]

Not all magnetos have an impulse coupling to retard timing at startup. Many engines only have the coupling on the left mag which is why many engines are started with only the left mag on.

I would expect if you went to two electronic ignition "magneto replacements", then "Both" would make sense.

But if you went to one electronic mag and kept one traditional mag(and the traditional mag does not have an impulse coupler), you would only want to start using the electronic mag.

[svyolo]

Most or all EFI/EI have a start function. Some set of parameters tells it the engine is not running, but then when you go to start, it knows you want to start. Some use a 12v signal to the computer from the start circuit, I think SDS EFI uses engine rotation (magnets "seen" by the crank trigger. My guess would be your Surefly uses the same, but the triggers are built into the unit. When its parameters are met for "starting", it retards the ignition, and if you have EFI, enriches the mixture (trimmed by engine temp).

It basically has the same function as "impulse coupling" on your starting magneto, but gets there a different way. Makes it easier to start, and reduces kickback. I can't see why you would only start on 1.