Not sure which bolts you mean, but red loctite has always worked well for my head bolts and exhaust header bolts. The bolts must be clean and dry when the loctite is used. Also the bolt holes need to be oil free.

If it's the head bolts that are loosening, then you might try some replacement bolts from Jet Model Products. They are better quality bolts. Heat is what makes red loctite let go, so you may be running a little lean.