I am chiming in with barely a year of experience getting my son started; however, I will say, you'd be shocked at how some of the smallest, seemingly simply things add up to make speed. My boy started fast and then plateaud. I kept pestering him about how he was driving and making sure he was not lifting or dragging the brake. But when all of those were no longer the issue, we started really diving in to the nitty gritty of the kart. A new chain. Cleaning the floorpan and parts between races. Cleaning or replacing the spark plug and chain. Every last bit of it, no matter how seemingly insignificant just started to add up (or take away, I suppose). It would be a tenth of a second here or a hudredth there. Basic maintenance alone went from him having his teeth kicked in and lapped, to at least on the lead lap and in contention. After that we were able to hone in one where to spend our money and effort in terms of set-up, tires, upgrades, and the like. Before you start looking for big problems, make sure its not the details.