Krisjan F, try this. Remove the airbox and filter. spray some carb cleaner into the carb throat. Close the choke and try to start the engine. If it fires, you have a fuel problem. start at the gas cap and clean the vent. Next, make sure the tank is clean and the gas is fresh and mixed to the correct ratio. make sure the filters and valve are clean in the petcock. check the fuel lines for any kinks or blockage. remove and thoroughly clean the carb, useing a piece of wire and carb cleaner.
if it does not fire, then you have either an electrical, or a compression problem. remove the spark plug. insert the spark plug into the spark plug boot. hold the base of the plug against the engine block. Turn the engine over as if you were starting it up.
Then check the magneto. points are a very common item to fail. and most times its because they are dirty, or out of adjustment. clean them with an emory board or a point file. An average gap to set the points to is .014"-.018". Coils rarely ever go bad. but, if the magneto is full of rust, every thing needs to be taken apart and cleaned.
if it has spark, then you have acompression issue. all 2 strokes must have at least 120 lbs of compression to run. Use a gauge to test the compression. If less than 120 lbs, you must find where it is going. The usual places are, rings, head gasket, cylinder base gasket, intake manifold (where it mounts to the cylinder), or crankseals. If compression is higher than 120 lbs, pull the exhaust system off and make sure the port and the pipe are clean. These two things will prevent starting. Hope this helps, good luck.