Sounds like someone gave you bad advice. Lots of people will do that when its not their engine at risk. With a new engine, put a slightly smaller prop on. If normal sized prop is 11-6, break it in with a 10-6 or so. Loading a new engine with a large prop and lean run will surely cook it. A fuel with castor content will also help. Yes, it will slobber up your model a bit more but all that oil blown out the exhaust is also carrying HEAT out of the engine.

You use the high speed needle to adjust the high end. It should always be set at peak RPM (the steady high pitched scream) then back off a bit until it's burbling a bit. With an ABN (aluminum piston, nickel-plated brass cylinder) you don't want to run it in a blubbery rich setting without letting the engine heat up initially or you WILL ruin it. Peak it out for 10 seconds then back off slightly.

When you idle down, the low speed needle takes effect. Let it idle a bit. What I do is briefly pinch the fuel line while idling. If the engine speeds up a bit, you're too rich on the low end. If too rich and you suddenly open up the throttle it will stumble. If the engine dies immediately, you are too lean on the low end. Open the low speed adjustment perhaps ¼ turn then try again. You may need to readjust the high speed needle.

Eventually you'll arrive at a proper setting.