Originally Posted by jyasaki
As I recall, there are some 2-stroke engines set to fire each plug every 180 degrees of crank revolution. Don't recall the reason, but they apparently are out there.
I would expect that you'd get correct readings on either 180 or 360 degree settings.
would that be on a twin cylinder with 180 crank?
that would make sense, one coil for two cylinders, so one plug gets a neg spark and the other a positive spark.
the "lost" spark on the cylinder at BDC doesn't lose much voltage because theres no compression, so the voltage required is low to jump the gap, leaving all the energy for the more difficult pressurised gap at TDC.
I did think this only worked on 4 strokes though, because whats stopping the lost spark igniting the crank case through the transfer port?
maybe the transfer port is still covered by the piston at 20-30 btdc that the plug fires at?
anyone know for sure, would be interested to know if any 2 cyl 2st engines use one coil.