If you have the unit stored where the average temp has been below 40 degrees, I would suspect that it is just a collection of moisture in the exhaust system. You have an air cooled system, which means the only liquid would be oil. Cloudily white could be moisture in the oil. A rule of thumb I have always told my students, black smoke means rich fuel mixture, blue smoke means oil, and white means water. If it is water, it should clear up when the engine run awhile at normal operating temperature.