High Idle

[Blue69Gen1]

Just installed a new Demon 750 vac secondary with electric choke on a new ZZ383 crate motor. I can't get the idle down below 1500 RPM's. Timing is set a 10° with vac advance disconnected. Throttle linkage is disconnected. The 4 idle mixture screws are all 1 turn out. I can turn them all in and it makes no difference on the idle speed. When I turn them out, the engine becomes noticably rich. Front and rear fuel bowls levels are set at the lowest mark on the sight glass. New Holley mechanical fuel pump that says it delivers 6-8 psi with no regulator required. The engine idles at 2000 rpm when cold and then after it get up to temp, it drops down to 1500. When I shut the engine off, it wants to diesel and spin backwards.

Thanks,