Because the hsn is as it states "high speed". By adjusting your lsn first you will get easier start ups & better take off from not being overly rich. But then again that's just me. To each his own. Many times I have read people talking about their motors dieing when they give it throttle after starting which is generally linked to having a rich lsn causing their motor to load up with fuel also giving trouble with restarting. This way it saves a bit of frustration & wear & tear on some parts like pullstart strings, owb's. I may have a little trouble on initial start ups from slight over primeing since I blow thru my pressure tube to prime my engine but once its warmed up my motors usually start up on the first or second pull or the first press of the roto start button.