Carbs are not rocket science...One of the biggest problems with new engines is trying to run with "factory" needle settings...If the carb is working properly and is set correctly a brand new engine will idle just as well as one that has been run for years....Only thing different is how loose the crank is and how well the rings seal...This will let the engine idle a little slower....
The key is how the carb is adjusted, not the length of time the engine has been run..PERIOD..
The high speed needle has absolutely nothing to do with how the engine idles...But the low speed needle, if opened too far, will affect the high speed needle setting...
Open both needles 2 turns, set the high for max rpm, then adjust the low, not the other way around....You should be able to get a good idle at 1800 rpm, with good transition, by leaning out the low needle a little at a time and re setting the idle speed as you go along...After the idle and transition are good the high speed needle may need to be re set...
If the reeds under the carb are not seating properly you will never get a good adjustment on the carb....