Check compression – if you have very low compression, there can be too little force in the crankcase to pull fuel through the reed from the carb and push it into the cylinder. Could also have the lower reed totally stuck or blocked by insect nest, but not likely.
Look for the easy to check stuff first! Before you go tearing the motor apart, check that lower for spark. Sometimes a motor can run a while on one cylinder without the dead spark plug getting wet.
Dave
