You have an oil injection system in it, right? (It uses straight gas, no premix)
The injection system may be leaking. I am not sure if this is 'normal' or how to fix it.
However, everyone I know stores their outboards in a vertical position, (never lying down) by clamping it to a workbench, hanging it by the garage rafters, etc.
This may be obvious, but if it only has this problem, lying down, consider changing your storage position, if possible.