on some lifts it is common for them to condensate in the exhaust system and there will be some moisture that comes out of the exhaust. As long as its not steaming or smells like coolant then there shouldn't be any problem with that little bit of condensation from the muffler.

As for the mixer? yes over time they will gum up and you can remove the mixer cap/diaphram assy and clean it with carb cleaner, clean out the gum in the throat of the body also. When you restart the engine it may be hard to start but once you start it hold the throttle wide open (at governed speed) till it clears up.

NOTE: if this unit has an O2 sensor on it go light with the cleaner, if you use too much it can foul up the sensor and you'll be replacing that as well.

As far as adjusting it, if there is a screw on the side of the mixer that is usually the air/fuel mixture screw. If you dont see one then it probably is ECU controlled.