Just did a '03 WR reserve petcock on a stock '02 YZ250. ('02-'08 stock 2.11 gallon tank) I tested the before and after volume with both petcocks and in various lean over angles. A few interesting things came out of this. First, the stock petcock/fuel capacity has some caveats. With the bike level, the tank drained exactly 2.0 gallons. With a +-20 degree angle, an extra 14 oz. or .11 gallons came out. That seems to be where Yamaha came up with 2.11 gallons......the bike leaning back and forth 20 degrees. Now it gets interesting. If you go to 40 degrees, you get another 13 oz. out or .1 gallons. If you go to 60 degrees, you get another 12 oz. or another .1 gallons. Beyond 60 degrees does nothing. So the bike, if you lean it over, has 2.3 gallons useable. Could be useful to know if you run out while on a trail etc., you could get another .3 gallons by leaning it over. One catch though. The tank on the petcock side only holds .15 gallons, so you have to lean it over twice to get the whole amount ie. run out of gas, lean it over, burn .15 gallon, run out of gas, lean it over, burn .15 gallon gas....clear as mud? So this means that the tank on the right side below the frame holds .3 gallons. Now, how about the reserve petcock? Remember that the tank on the petcock side holds .15 gallons and that there is an extra .1, .2 and .3 gallons at 20, 40 and 60 degrees of lean. The on function on the reserve petcock shuts off flow at exactly 1.85 gallons. That may not sound like much of a difference, but you don't get the "lean over" benefit in "on" because the "on" petcock tube is right where the frame separates the tank. So by using "on", you effectively get a 1.85 gallon range with .45 gallon reserve. Not bad. Enough to get you another 10mi.+ to get to gas. Which petcocks work? '99-'06 WR400/426/450 and '01-'06 WR250, $15 at the TT OEM store.