I'm interested in this as well... I bought a FS 90 AR That cranks and fires but will not continue to run. Spray starting fluid down the carb and I can get it to run for a a few seconds so I think I need a carb rebuild. I can get a kit off fleabay for ~$10. How difficult is this?The needle valve is stuck open or not closing completely on the seat, could be from debris or the diaphragm could be worn. You will need to tear down the carb and inspect. Get a clean work surface and take your time making sure to keep track of the order you remove items(if you have a digital cam take pics of each step so you can remember how it goes back)
Good luck post back once you have it open and let us know what you find.