There's many factors that go into getting long run times per tank
For me having the right tune on the motor, right pipe, and right clutch setup for the track is one factor. Having a smooth throttle finger is the next factor (usually harder to do but worth it) and is looked at as being one of the biggest factors. Usually doing that much will help, there are many others that can be factored in and will all play a part in having the run time needed or not. I like Jammin's brakedown on pittting in the above post. It does make the most sence if running that long of a main. In my area most club races are either 15 or 20 minutes for a main. Long enough to pit once or twice, but not long enough to win or loose by pitting strategy.