I've been doing some lighting work on my quad which hasn't ran in a while. I finished the lights earlier today and started it up and has a sweet and bitter smell coming out the muffler. I first noticed vapor coming off of the header pipe near where it connects to the cylinder. Checked bolts, all tight. My coolant seemed to drop slightly below the full mark which happened before today. I've heard it could be a bad head gasket or header gasket. Anyone know before I tear my motor apart?