Always adjust timing before the carb(s). It sounds like a carb issue for sure. Disconnect the outboards and I’d suggest taking a flat blade screwdriver and go down past the boosters on the outboards and tap the throttle plates to verify they’re closed. Then tune just off the center to get the idle you want. Once that’s set you can look at the outboards. I’ve had the gaskets hang one outboard open and the engine will run off just that.
I actually forgot about the suggestion to disconnect the outboards, so I'll try that today. Obviously there are a lot of moving parts and many different things to try, so I hope nobody thinks I'm ignoring any advice given...
