That is correct! On most of the YS motors the regulator controlled the low end and mid range. The newer motors have a low end adjustment also.
Make sure you have the fuel and pressure nipples plumbed correctly. After running at half throttle you should shut down and if you disconnect the pressure side of the tank, you shoul get a very audible hiss of pressure release.
Start with the regulator screw flush with the housing and hi end needle about 2 1/2 turns out. bring up to full throttle and adjust for max rpm. Bring to idle and check transition. If slow then turn brass screw in about an 1/8th at a time until you get smooth transition. Always readjust the top end after each low end adjustment.
You should contemplate changing out those Orings! It will help.