So are you riding it before it is fully warmed up, it has to be at operating temperature before you attempt to adjust the idle.
What did you set the float level at, and how.
Have you read the manual, or do you not have one, I can get you a free one if you wish.
Pulling the plug will tell you nothing, you need to do a plug chop run.
If the air screw is at 2 1/2 turns out, either the pilot is wrong, the choke is on, the air filter blocked or you are flooding.