1. Warm engine up.
2. Kill engine.
3. Install brand new never used spark plug.
4. Start up Blaster and immediately run through all 6 gears wide open throttle. When you reach the top of 6th, pull in clutch and kill engine.
5. Roll to a stop with engine off.
6. Pull plug.
If plug is tan color or lighter, go up a size on main jet. If it is almost black to black, go down one main jet size. If it is a medium brown (Starbucks coffee+ 6 creams), it is right on. Repeat process until coffee color is achieved.
That is IF your carb is clean and you have no air leaks.