Could of sheared a flywheel key, likes to happen on a backfire event too, It will effect ignition timing and make it backfire but spark will still be good at the spark plugs.
I guess if it's sparking both spark plugs when you test it, then you could rule out the start stop switch, cdi would still be a possibility and so would the flywheel keyway.
To Check the keyway you gotta pull the flywheel, don't try what my buddy did and just pull the cover and FW bolt and look at the keyway. His looked fine but was sheared.
I have a defective cdi you can barrow if needed. It will start your ski no problem just develops secondary ignition misfire when you ride and it get warm.
Nothing wrong with checking reeds, they need to seal, but would seem odd they failed just like that.
I did a diag for another member, no start and backfire, I found his just purchased eBay stator was putting his cranking timing at 60 plus degrees out.
