There are a couple possibilities on the leak.
First determine approximately where the leak is.
Look around and under the carb. If fuel is coming out around the bowl gasket, or dripping out the air inlet, or the drain hole under the air inlet, the carb is flooding. That is caused by the needle/seat valve not stopping the flow of fuel once the bowl is full. It can be caused by trash in the needle/seat, a worn needle/seat, the float set too high, or the float partially sunk, as in gas had gotten in one of the pontoons.
The other cause can be the fuel line connection. Clean the area around the line and fitting, use some carb cleaner, compressed air, rag, whatever it takes to get a good view. You will probably need a good flashlight, possibly a mirror to see, but look for fuel leaking around the fuel line connection. It could be as simple as needing to be tightened, or it could be a cracked line, cracked fitting, or cross threaded fitting. If you cannot stop the leak by tightening, and it has to come apart, be extremely careful not to get any trash in the line of fitting. Before reconnecting, turn on the fuel and let the line flush.
As for adjusting, that will be the last thing you will do. The carb needs to be working correctly, no flooding, air cleaner serviced, fresh oil, good clean fresh gas, the engine properly tuned, valves adjusted, thermostat working, and good compression on all cylinders. Many times an innocent carb is blamed for a multitude of problems!
Once you are ready to adjust, get the engine up to temperature.
Set the idle speed to around 500 RPM.
Locate the idle mix screw. It will be the small screw up by the mount flange. Turning the screw out leans the mix, in richens it. Turn the screw out until the engine falters, then slowly in until it runs smoothest, then in about another 1/16-1/8 turn.
If it has a main jet adjustment, it will be a larger screw on the bottom or on top of the bowl cover. Turning the screw in leans the mix, out richens it. Turn the screw in about a turn. With the engine at idle, quickly push the speed control lever to full throttle, listen for the engine reaction. If the engine doesn't hesitate, return ti idle, turn the mix screw in further until it falters on sudden acceleration. If it hesitates, back the main screw out 1/4 turn, repeat the test. Keep doing this, richening the mix until the engine takes sudden throttle without hesitation. A single puff of black smoke is desirable.
Again, all this is dependent on the rest of the engine being right, especially the points, plugs, timing, plug wires, etc.
Let us know what you find. If the carb needs to come apart, don't be afraid of it. They are simple and field serviceable.
