First off, there is no such thing as a standard setting on those carburetors. Initial settings are suggested to just get it up and running before you can make a better more accurate adjustment although it may work fine on factory initial adjustment.
You might want to turn the main jet adjustment in all the way until it bottoms while counting the turns just for the record. Then back it out to where you originally had it.
Then start engine and allow it to warm up at moderate speed for a while. Now, pull throttle to full rpms which should be right close to 1800 rpm's. Turn main jet needle in until engine slows or starts to stumble. Then turn it out until it runs smooth and give it another half turn out.
If it smokes black after doing that, you have carburetor problems. Dirty, oversized main jet, fluel level too high etc.
Now adjust low idle speed and air mixture. The air mix should adjust up from half turn out to maybe two turns. If not, carb problems.
If it still stumbles under load, you make sure you have full fuel flow out the bottom drain plug on carburetor. Let it drain for a minute or so to make sure good supply continues.
Don't over look ign timing. Top dead center static timing (meaning engine not running) and then check advance of spark when running at full throttle. . Should be 40 degrees factory battery ignition, 30 degrees with flat head over size (3 7/16) pistons is best but 40 works ok for most, or 22 degrees with fire crater style dome piston all considering gasoline head.
If magneto, impulse snaps just a degree or two up to five degrees after top dead center and close to 35 degree advance of spark at all engine speeds