[dewzer]

The wrong spark plug gap will cause a world of hurt on a man. Air flow restriction to the carb. is another. Last, a partally plugged exhaust.
Your on the right track by adjusting the valves but it sounds like a carb issue.
When the float pushes the needle up into its seat the float should be level with the carb itself.
With the carb off and the needle and float installed, flip the carb upside down and make sure the float sits level or just a tad higher on the opposite end of the needle. There is a bendable tab that pushes the needle into its seat to make adjustments.
To high a float adjustment will cause the situation you describe.