I usually run just enough to put me close to the legal fuel capacity. If you don't have a way to check capacity or are not worried about it, I would just run the minimum amount it takes to get from the carb to the tank. The more tubing you run the leaner the motor gets. Its like a water hose, the longer the hose, the less pressure you get at the end. Eventually, if its too long, you won't be able to tune it.