Magneto's
Slatch has posted a good answer.
I would like to add a little. If you ever get rough running in flight with this magneto set up it is most commonly, but not always, a faulty left impulse magneto.
So when doing routine magneto checks always check the right one first by selecting from both - right - both - left - both. If this is ingrained to the thought process on routine checks if a pilot ever has to do it in flight then the right is normally most likely to be the good one and it will assist in the rough running drills should they ever be needed.
MM