Hello Rover Community, I'm hoping you can help me out. I am new to the series world, and learning as I go. Please see the video below for current running condition, followed by an explanation.

https://youtube.com/shorts/-w1G8o39K5E?feature=share

I've been fostering a IIA 109 pickup for my friend Bill Simone's family since his passing 10 years ago. I get it out of the garage every now and then to give it some exercise. For some time now, the truck has been running rich at idle. Fuel mixture screw on the Zenith carburetor changed nothing. Recently, I've been motivated to try and resolve the problem to get this truck running as well as it did 10 years ago. I started with a new carburetor to try and resolve the issue. No change. Idle mixture screw makes no change to how the truck runs. I went through and set valve tappet clearances, and then double checked. I started to suspect ignition problems. The truck is fitted with a rebuilt Lucas 25D from Advanced Distributors with electronic conversation, and a Crane Cams Fireball XR700 Ignition module. I replaced the coil, wires, plugs, cap and rotor arm. Plugs get fouled up pretty quickly because of how rich the engine is running. I've been cleaning them up and checking gap every now and then during this diagnostics journey. Based on the workshop manual, since I'm running 90 octane ethanol free fuel, base timing is supposed to be set to TDC with vacuum advance disconnected, which is where I currently have it set. Compression test shows 120psi in each cylinder. Yesterday, during a test drive, engine speed was increasing while applying the brake peddle. I started to suspect a vacuum leak. This morning, I hooked up a vacuum gauge directly to the intake manifold. Very low and erratic vacuum. I sprayed carb cleaner around the intake manifold in hopes I would find a failing intake gasket. I couldn't get a jump out of the RPMs.

I'm struggling to determine next steps for troubleshooting. Any help that can be offered would be greatly appreciated.