Since you are sure you have the carb jets and floats adjusted properly, you might consider checking for a weak spark when the motor is cranking but not starting. A weak spark can cause the flooding you describe.
Is it possible that the motor is not actually flooding but is overloading on oil? If the oil injection system has a faulty check valve, the motor will be hard to start and smoke a lot at startup until the excess oil is burned off. Just a thought as this was a problem that I had on my motor previously. Here is a thread discussing that.