There is a gear drive pump behind the clutch. The clutch drives the oil pump. The amount of oil is control ed by a valve on the front of the motor. The more RPM, the more oil is put into the line...
Check for spark, check that the plug is clean, see if you have fuel, see if the carb is clean, see if you have compression.
If you have all that, it should start.
If it runs bad, you might need to...