Does it look like mine in the beginning post? If it came from an FS-75, it is a 25.4cc. I haven't been able to finish mine and run it, but I am positive it is going to be a good "runner". Nice size ports and port timings.

Here is a copy of the owners manual for the FS-75: http://www.stihlusa.com/stihl_owners...S75_Manual.pdf

In the future, to get displacement, just measure the bore and stroke. Then use this forumula: (bore x bore) x stroke x .7854 = cubic inch displacement (If you measured in inches.) Then just divide that result by .061 to get cc's.

AV8TOR