stock fl250 is a 70 mm bore and a 64.4 mm stroke. So using the formula for a cylinder (pi x r^2 x h = cc), if you increase the bore to 71.5mm (each .020"=.5mm) the volume of the cylinder becomes 258.575. That isn't quite 280cc. To get to 280 cc you'd have to take the cylinder out to 74.5mm, which isn't possible since the largest piston available for the 250 is a 72mm.

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