The different quality levels set requirements with regard to properties such as minimum lubrication, minimum detergency, maximum smoke and maximum deposits.
A two stroke engine oil is granted the official JASO seal if it has been independently tested.
JASO FA – original spec established regulating lubricity, detergency, initial torque, exhaust smoke and exhaust system blocking.
JASO FC – lubricity and initial torque requirements same as FB, however far higher requirements over FB with regard to detergency, exhaust smoke and exhaust system blocking.
JASO FD - same as FC, except with far higher detergency requirement.