2007 70Hp yamaha

Just purchased a 2007 1720 Key West with an 07 Yamaha, first trip out I noticed the motor was very loud, when I got home and started washing things up I noticed a lot of exhaust soot around the transom so I started thinking exhaust leak; pulled the cowling and it’s as clean as new,,,,, any ideas with this Yamey??????

Start with a compression check. Over fueling could be bad fuel pump or primer pump diaphragm. Half tilt the motor with the intake silencer off, squeeze the primer bulb normally to see if fuel runs out of the carbs. Shouldn't be any. The other possibility is the primer coil which shuts down the enrichment as the motor warms up. You can test that off the carb on a battery. Needle should extend after a minute.
If the motor is not running at the optimal air/fuel ratio, therefore less efficient, you will be compensating with more than normal throttle opening and the motor will sound louder than normal.