Pretty severe I would say. In the field, we call a lack of fuel in the mixture being burnt, a "lean" condition. When you engine is running lean, you run the risk of causing extreme engine damage in both the immediate and distant futures. With that in mind, always keep up on your engine's maintenance. There needs to be a certain amount of diligence here, so let's keep our engines running smooth and efficient. After all, they ARE pulling our weight around to transport us on a daily basis.