If you have overflow tubes and the accompanying drain manifold, air currents act to evaporate the gas quite quickly. Not only does this make starting after sitting a bit difficult, it leaves a deposit each time this happens. What I did was to put a down loop of the manifold drain under the oil fill, then routed it over the swing arm pivot. I put enough oil in it to show about an inch at the bottom of the loop. This prevents air from circulating through the carbbies and exiting at the vents. If your loop is not deep enough, spirited riding will tend to empty the loop.
