Second from the top to start. When close to good your bicycle motor should run in a clean two cycle on any pull, up through full throttle. When you are on a slight down hill or barely cruising along it will be breaking in and out of a four cycle/two cycle.

If you lean it out enough to run in a two cycle all the time you lose power and engine longevity.

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If it ain't broke, and you mess with it long enough, it will be.