Don't think this would slow you down, but 20:1 is crazy oil rich, and will carbon up your exhaust port and pipe quick. Anywhere from 32:1 to 50:1 is fine. If I remember right this is a single speed moped, and they just don't have the power for hills, especially if you are on the heavier side. Repack wheel bearings, and be sure tires are properly inflated. Remember, this is a comfortable bicycle, NOT a slow motorcycle. Fix your air leak before messing with jetting.