Yeah, the 12:1 disc is literally the entire size of the inside chamber in the FMU with no ring. Must be a 10:1 disc setup. I had my car go crazy lean when I was having a gasket leak on my old FMU. Once you take them apart so many times they get harder and harder to seal up perfectly. Make certain you have absolutely NO vacuum leaks from the intake manifold to the FMU too.