I have both a Du4 Duplex, and a Du4 dual (not 2 spark) they have different names and different looking points covers. What is the difference between the two? I thought that they both enable you to start on battery, then switch over to magneto. Both mags are the early brass Du4s.
I'm really curious how these work
I believe the duplex has a commutator and requires a separate coil connected to the switch while the dual can operate with a coil or without. My Chalmers-Detroit has a dual magneto and I can start and run on the coils in the Heinze coil box or start and run on the magneto. I use an impulse to crank start on magneto because it is hard to spin a 40 hp motor without a compression release but starting on the coils is a snap.