I have an old OS 90 that has too much compression causing backfiring and throwing the prop. How can I get head shims to reduce the compression.

Thanks
Bob

Cylinder head gaskets can be easily made from brass shim stock. Just take the existing cylinder head gasket and use it as a pattern to cut out new ones. You can use a sharp Xacto knife to cut them out. Hone them on a fine stone to remove any burrs.

You can obtain shim stock in a wide variety of thicknesses. K&S sells brass sheet in a variety of thicknesses, and you can buy them at many hobby retailers or crafts stores. If all else fails, try a machine shop.

Another alternative would be to locate regular O.S. gasket sets for your engine. If you let us know which particular engine you have, we can see if any of the current-production gaskets might work.