Let me just step in as the voice of our one and only Gregger. Once when I was having trouble determining the cause of performance issues with my bike, Greg chimed in and said...
Here is a seat of the pants test to check for proper main jet size. On a long straight (free from the local police), wind the bike out in 4th or 5th. Get it above 5000rpms accelerating hard and then slightly back off the throttle. If the bike seems to pick up speed, your mains are too small. The opposite, too big. Nothing and you are just right.
It really does work as a quick and easy means to determine if your jet size is working for your bike's setup.
