The behavior you describe sounds like the main needle may be too lean. I tend to over lean this engine a bit when tuning by ear because if you are used to the smaller engines, you tend to tune them until they scream. This engine never gets the high pitched whine like the small glow engines.
I run a 18x10 prop on low nitro fuel (between 0 and 5%). I have used a Cline regulator in the past, but it was sticking open so I have now removed it and my 180 runs fine without it.
ajcoholic is right about break-in. Mine was not right until 5 gallons of fuel.
Also, make sure you use large fuel tubing. ANd a large clunk in the tank. Disconnect the tube from the carburetor and connect about 8 inches of tubing. let it hang down below the tank and let it siphon into a measuring cup. It should flow at a rate of several ounces per minute. If there is some constriction in the system, the thirsty Moki will lean out in flight.