RE: K&B .65 Sportster (yup, more from me)
You must set the high speed needle for max rpm, minus 200-300 rpm with only an ounce of fuel in the tank. Then the engine's mixture will remain rich enough to prevent sagging as you burn off the fuel in the tank. Yes, the engine will sound rich when you fill the tank and restart after setting it this way. DON'T TOUCH THE NEEDLE VALVE! If you do, you'll be right back to sagging when away from shore after initial launch.
This happens because your engine uses suction to pull fuel to the carb. This is a very weak force and it is sensitive to the fuel pressure head.
Ed Cregger