Re: Just a few questions...
When looking at the ratio of oil to gasoline, the larger number represents the gasoline, the smaller the oil.
A 24:1 ratio, which we recommend for break in, means 24 parts gasoline to 1 part oil. Your Harley riding prof is mistaken about the 12:1 recommendation. That will be way too much oil and will cause you more problems than a little "black goo".
Your carburetor should have an idle speed screw to set/adjust the idle speed. Try that, as was suggested above.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"