I'm running hemi head predator and I replace stock thick head gasket with thin head gasket and I'm having trouble setting lash. I first set lash at 0 so there was no pressure on push rods I could roll rod with my fingers freely. The kart would only hit 5700 rpm so I loosened valves and got it to Rev higher about 6300 rpm but would not hit 6300 every time I Rev ed it up would be between 5900 and 6300. Any idea what lash should be.