Your new head gasket will only work as well as you have managed to clean the old head gasket off your engine block. Any leftover portions will interfere with the ability of your new one to seal and cause endless problems with vacuum and oil leaks. Cleaning off the old head gasket requires great care; you can easily damage the engine block through scratching and scoring. The smallest scratch can also ruin the seal of a new gasket.
Hold a razor blade at a 45-degree angle and gently slide it under the gasket, moving it back and forth (but not scraping the metal) to remove as much of the old head gasket as possible. If you can grab a bit of the gasket with your fingers, pull it up and toward you while pushing the sharp edge of the razor blade along the base to try and peel it away.
Saturate the remaining old head gasket with carburetor spray. Wait about five minutes, and spray it again.
Lightly scrub the old gasket with a plastic dish scouring pad.
Continue spraying the old gasket with carburetor cleaner and scrubbing with the plastic pad until the entire surface is clean of the gasket and any residue. A good way to test that you have it all off is to run your finger over the surface--you'll be able to feel any bumps made by remaining residue that your eye can not see.
