I looked as well and had the same result. I did look in my KLR650 service manual and it has a 40mm carb. bore. When I do the math for the ratio bore area/displacement 1256.6mm^2/651cc = 1.93mm^2/1cc so for one cylinder at 250cc the carb bore area would be 482.5mm^2 so the bore would be 25mm. yet the GS500 has 34mm bore carbs. great for max power and rpm, but not so good for fuel economy. what I have not found is the intake port area/diameter for the intake port.
