[deadmotor]

I have a 1993 115 Yamaha that ran perfect forever then last time out it slowed while underway and barely made it back to the ramp. I changed the fuel filters, the fuel separator, and rebuilt the carbs. It won't start anymore, it spins fine, has good compression and I am certain its getting fuel but it just spins and occasionally backfires. I'm a long time mechanic but not a outboard mechanic and I'm thinking it has to be ignition, but??? I need help from someone who knows Yamaha's.
Thanks
Deadmotor

[JB]

Backfires?

Is that a cough in the carbs or is it a loud bang from the exhaust?

A loud bang suggests it is out of time. A common cause of this is a sheared flywheel key and a shifted flywheel.

[Ray Neudecker]

Start with a timing light and see what is happening with fire.