Re: 89 200 XP "Sneezing" (Rude520)
timing would be a good place to start. Verify your idle timing with the motor warm and in the water with back pressure. Sneezing could be caused by a few things but I'd start by looking at the carbs. I would also inspect the throttle roller on the port throttle body. If there is just a hard black plastic roller then the clear cover roller is probably missing or has deteriorated. You need to make sure that the throttle plates are opening fully at wide open throttle. I would also remove one of the recirc valves and check its condition. They are a one way check valve that scavenges unburned fuel and sends it to the cylinders to improve idle characteristics. A quick test for the recircs is to run the motor on cooling muffs and raise the motor from full down trim to full up trim while watching the tach and listening to the motor. Any change in RPM's or pitch indicate plugged recirc valves.
40:1 is a little heavy for that motor 50:1 is the prescribed ratio. And use Champion plugs QL77JC4's gapped at .030".