When you adjust the low speed mixture, turn in till you get the highest idle, then turn back out till the idle drops. If you leave that mixture it at the higher idle your too lean for cold starts. If you've adjusted the idle speed via the stop screw you will probably need to adjust that as well. Get those dialed in and then move onto the high speed mixture. If you had three hands you could adjust the high speed under load. For the high speed mixture you want to turn in till you hit the highest RPM then turn out till that starts to drop. Now test under load. If your too rich you'll hear a bog, the RPMs won't climb, the clutch won't lock in, and you might see or smell unburnt fuel.