RE: saito 120
Your friend should have the manual for that engine. The low speed adjustment is a small flat Brass head screw on the throttle linkage arm. It is not! a phillip's or hex head screw. It is located diredtly on the opposite side if the clevis arm, in the center, directly center.
Adjustments are made by rotating the screw counter clockwise for rich and clockwise for lean. Use very small increments, meaning 1'32". Not much is necessary. Then readjust the high end.