Good info from DMcQuinn, but one thing he said sounded a little confusing to me, so I'll clarify it a little in case it confused you too.

Turn the needle valve in till the engine runs at its highest RPM - Now let's say the needle is at 10 O'Clock, as you keep turning, the rpm will not change (or will change VERY little). Then, at 12 O'Clock you hear the RPM start to drop. You should return the needle to the 10 O'Clock position, and maybe 1 or two clicks toward 9 O'Clock

Also, if you are breaking in the engine, turn the needle back to 9 - maybe even 8 or 7 O'Clock so it's running fairly rich, but not sickly rich. Do that for about 2 tankfuls and you'll be fine.