Hello,
If you remove the muffler, you can stick a popcicle stick into the exhust and gently turn the engine to mark it. Remove the stick and measure the distance from the mark to the end. This is the bore. Using a probe of some sort and a marker, you can do the same thing to find the stroke. With the piston at the bottom of the stroke, mark the stick at a fixed point on the cylinder head. With the piston at the top of the stroke mark the stick again. Subtract this measurent from the first and you have the stroke. Put both numbers into the displacement calulator at the link below and you will have the displacement. Don't forget to select only only one cylinder. Perth being close to the equador must be warm, right?


http://home.earthlink.net/~jalby/puter.htm

Dave