i have a 50cc Pilot Yak 54 and trying to set up pull pull rudder. What size servo arm did anyone use and did it have offset to keep the cables from going slack. Tried a 3" straight and it will not work. Tried crossing cables and tried straight always has slack one side or the other

Whatever the control horn width and offset is, it is best to match. If at all possible get the control horn pivot hole right on the hinge line so that no offset is required.