I'm with the guys above, you are chasing a gear problem that doesn't exist. With a green plate, obviously your driver is very young and new. Focus on seat time and handling first. Gear it to peak around 5800-6000rpm max and work on everything else. What chassis are you on? If you're on a 15 year old antique and the rest of the field is on new stuff you are going to get outran every time. What tires? How old are they? I coach many new karters at our local track to put the best tires and chassis under their kid as possible. It instills confidence and good handling will make it easy to drive so it takes away their fear. So many new dads go into it thinking " he's just starting out, so I threw these 10 year old bricks on it for seat time, I'll spend money on tires once he's better and I know he's going to stick with it".
Don't be that dad!
Tires
Chassis
Setup
Driving
Motor
In that order!