As a base setting turn the mixture needles all the way in and then turn the high speed (closest to the air filter) screw 1 3/4 turns out. Set the low speed screw 1 1/2 turns out (the screw closest to the manifold). This will be a close starting point. Start the bike and set the low speed mixture in conjunction with the idle speed screw to give the lowest reliable idle that still has a crisp responce when you rev it. With the bike on the stand rev the engine to full throttle and adjust the high speed mixture to give peak revs then richen (wind out) 1/8 turn. Do this abit at a time so the engine isn't just sitting there screaming. This should get you pretty close with fine adjustment (normally no more than 1/16 to 1/8 turn) done while riding to get it spot on. Check the colour of the plug (should be light tan, white is lean dark brown is rich) to make sure its not lean and enjoy!
Hope this helps

Matt.

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Black PR50 #52.