It could be a 21cc, or it could be a 24cc. (23.6) The next size up, the 25cc has larger fins and the fins have holes in them to go down through with a long allen wrench to undo the cylinder bolts.

If you're interested, here's how you can measure it. Take the plug out, and carefully measure how far the piston travels from top dead center to bottom dead center. It's a little tricky with that angled plug hole, but it can be done. I use the back end of a vernier caliper to make the measurement.

Then take the muffler off, and put a pencil, or a dowel with a rounded off end into the exhaust port, straight over touching the other side of the cylinder. Now rotate the engine so that the piston comes up and pushes against the dowel or pencil, hard enough up against the top center of the exhaust port to make a mark on the wood. Now measure that distance on your dowel or pencil.

You now have the bore and stroke dimensions. Use this formula: (bore x bore) x stroke x .7854 to get your displacement, or engine size. If you measured in inches, your result will be in cubic inches. Divide that by .061 to arrive at cc's.

AV8TOR