If you have a variety of classes and speeds you could use the Pursuit format to make an interesting and competitive race. We used it for all our races for many years.
Time the practice for the karts involved and then sort them by their fastest lap.
Take the slowest karts lap time and calculate how many laps they could do in the time you have in your schedule. That is the number of laps in the race.
Take the lap time of all the other karts and multiply it by the number of laps.
The amount less than the slowest karts total race time is how long they must wait to start.
All karts start from the pit lane.
You have to decide if you want to worry about people “breaking out” by going too fast, we never did.
It was sometimes necessary to assign a time to a kart that had trouble in practice.
In theory, all karts will finish at the same time if everybody drives every lap like their best. In practice, we did have a fair amount of the field finish on the lead lap for our 20 minute races. It’s fun to watch a race that gets MORE exciting as it goes along instead of less.