Well, After 4 gallons the engine starts to show its full potential.. The low end is more than you can imagine. I use half throttle in order to clear jumps right after a tight turn. The motor starts in seconds and idles forever! The carb settings are richer than suggested and still the power is more than enough. I ve seen engines in my local truck that give up at 4 gallons and my 621T had no flame out from day one. As soon as you find card settings the engine does not flame...ever!..Works like an e motor..haha its like switching ON - OFF!