I want to bump up my compression a little. Is it a good idea to do this? the block is not decked. Whats the most material I can take off? will I have detonation problems? thnks

Is it a good idea? Yes, usually, and especially if you have a matching camshaft for the desired compression. Unless you have domed pistons, a 76 cc head yeilds very low compression with stock pistons. Do you kinow what pistons you have?

If your heads are virgin and haven't been milled before, you can shave about .010" off without any problems. You can mill more, but you run into having to mill your intake, and possible valve train geometry issues.
A .020" steel shim head gasket will also help instead of the standard Felpro type for raising compression.
Here's a web site to calculate CR's

http://www.thedirtforum.com/millcalc.htm

But first Lets figure out what you have.
http://www.thedirtforum.com/Cidcalc.htm