All of the above descriptions have failed to mention he needs to add a return spring to the throttle arm.
Also, the lock nut atop the throttle arm needs to be loosened & a nylon washer or washers added to take up the slack in the loosened assembly.
The throttle arm has a small return spring already installed out of the box. Most non-homemade karts have a wound spring on the pedal that acts as the return spring, or a spring on the throttle rod itself that acts as a return spring. The stock/already installed return spring is a little weak though, and if you don't already have another spring on the kart somewhere in addition to the one on the engine, then these other springs will help make the throttle return back to "turtle mode".
If you can press on the gas pedal, then when you release, the throttle goes ALL the way back to 'turtle/closed butterfly', then you have accomplished the goal.
If you press on the gas pedal, but the throttle will partially return (eg you can still move the throttle back to turtle mode by hand after nothing is touching the gas pedal) then you will need one of these extra springs. I have seen them connected to a small hole drilled in the muffler heat sheild (not the muffler itself) and the example of the one connected to the recoil shroud is what I also did to my mini bike.
