Mariner 55 hp 2 stroke backfires won’t start ?

[Marti72]

Hi guys, I have a mariner 55 HP 2 Stoke 1990? And it will not start, electric start seems to work correctly and I did have it running first time every time, now it will not starts and backfires through the exhaust, and ideas, I have put in new plugs and cleaned the two carbs. Any ideas please

 

[racerone]

Plug wires on wrong or perhaps a sheared flywheel key.