Unfortunately Stihl no longer supports the FS 250. If the p&c are good it is likely a coil or carb issue. The coil is about $60.00, I may have one. Carb kits are cheap. I would recommend not buying Chinese on these two parts as they generally junk. As always dump the old fuel, change the filter and add some canned mix or regular mix with some Mechanic in a Bottle (helps to soften the rubber carb internals), change the plug and check for spark. If you use M in a B then let it sit overnight in the carb and flush. (I will bring a box of parts).
In my opinion the FS 250 is a great machine. I have two running plus a box of parts that was my first one (bought new). I recently purchased a Stihl 40-4 line head. It uses heavy short lines that are inserted from the outside and just pulled through when they are worn down. Love it.