Does it have stock injectors in there? And the reason it's showing lean when you hit the gas may be because of rich mis-fires. When you get the mixture much over 10:1, the fuel will fail to start to ignite. When you get a failed to ignite mixture, it will actually show a LEAN situation on the AFR gauge because you have a bunch of air that didn't get combined with fuel. So even though you're rich, it shows lean. Also, have you tried pinching the INCOMING fuel line to reduce fuel pressure and see if the AFR'S come up?