Fuel burns most efficently at a specific range. (I forget exactly but it is some where around 14:1. The jetting and other adjustments on the carburator are set to keep it at that range. Unless you change altitude, or make some other modifications that change the amount of air you get into the engine re jetting won't help. Too rich and you will foul plugs, too lean and you can burn a hole in the piston. Either one will cause a loss of power. Reading the spark plug is a good way to guage how rich or lean the engine is running. a Lt tan color is good. Darker brown to black is too rich. White is usually too lean. The main jet determines how much fuel you get at full throttle. The position and taper of the jet needle is where you get your mid range mixture. Throttle slide cut away gives youI'm new to the site a quick question I still have orginal jet in my bike would changing it make a big power difference. All part exept tires since new 6 yrs ago and looking for ideas on power upgrades.