The problem is your motor isn't starting then. Clutch would be engagedment, and if the piston is cranking and the motor isn't staring that could be any number of problems.
Since you said it was running fine before I will take your fuel mixture out of the list, and you probably know how to work the choke to...
SO, feel free to check any of the following for why it won't start:
Fuel flow, fuel filter, carb needle, air filter, spark plug, spark coil, kill switch, and all wires.
You need fuel, air, and a spark to run, make sure your engine is getting them all.