It's going to be hard to tune if you don't know if you are running rich or lean at the present. How will you know when it's just right if you don't have the right testing equipment available?

Flat top SU's? Are they actually SU carbs, or Hitachi's which are different & do not readily take SU needles?
If they are actually SU carbs, then there should be a wide selection of needles available, but not so good for the Hitachi carbs.