It's leaking fuel out of the carberatetor ,on a 18hr Kohler engine

The fill plug is on backside of engine, dip stick is on front. Page 3 page 8. If the carb float does not shut off you need to replace carb, this will stop fuel from flowing and into engine oil.

http://kohlerengines.com/engines/onlinecatalog/pdf/OM_3000_SERIES_18_590_09_REV_A_English.pdf

Dale either the float is sticking in carb. and needle and seat are faulty, clean/rebuild carb., or if equipped the carb. solenoid can stick allowing gas into engine, replace solenoid. Check the attached links,instruction and guides, Good luck
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The needle and seat in the carburetor are not sealing. If you don't want to have the carburetor rebuilt what you need to do is change the oil and install an inline fuel shut off valve in the fuel line so you can turn the gas off when the mower is not running or in use.

Dirt in float bowl, and it causes float not to settle back down.so the needle valve will not shut off fuel flow. The needle valve is on the bottom of float, when it gets enough of fuel the float rises and shuts off fuel until it needs more. God-BLESS! You may have to reset float.

look on the carb float bowl to see if there is a solenoid on it Make sure the wires are still connected and working. The float itself may be leaking allowing fuel to fill it. The metering valve...attached te float may be leaking too.

there's a tiny little piston valve called a Float valve inside carb just above the Bowl (cup) this shuts off fuel when engine is not using it ,im gonna say thats your problem this usually requires a little adjustment to get it right , ck out my youtube video on adjusting carb floats for my tip's n triicks on how to do this

Cut the water off (just to keep from wasting water), remove the float and see if water has leaked into the float so that it became too heavy to rise with the water and turn the water off.
Everything else works because you can lift the float and shut off the water. The valve could be sticking in which case, replace or remove and lube with a bit plumber's silicon.

The carburetor probably needs cleaning -- the float is sticking.

Charlie