i currently have about 100 miles on my bike as i just get a chance to ride at the weekends at the moment, i am not sure about the gas mileage but am still have about half the engines tank left in my 1 gallon red jerry tank.
Check your brakes when i first set it up i had my own too tight the pads were just catching the rims but a couple of quick adjustments and the bike seems to ride better.
the speedo shows i have clocked at 33 mph riding the 13 tooth gear, but i backed off as the front suspension forks felt pretty fragile, anyhow i enjoy cruising around at the 20 - 25 mile mark, the bike and engine seem to handle better in that range.
Breaking in, the elders say it takes close to 1000 miles, thats alot of riding but i am going to follow everyones advice and wait before i start putting add ons to the engine. I might try and add a couple of inchs of silcone hose to help quieten down the engine abit.
kawaski i like the add on tank setup you have do you have it blogged anywhere, if not where did you get the tank, is it gravity fed all the usual questions that rookie builders ask sorry.