I think you need the vacuum retard connected and programmed properly to solve the problem. The stock 123 is programmed for vacuum advance which is wrong for B20B and B20E engines - it should be vacuum retard. When you connect the stock vacuum port (retard port) up to the distributor it totally screws up the timing. From what I can tell everyone using a 123 with either of these engines has pulled the vacuum line to get it to run.

I think most people associate vacuum retard with emissions control and feel it's OK, perhaps preferable, to disconnect it. It is indeed part of the emissions control, but it also serves a vital function just like vacuum advance, namely to give a quick boost to the timing advance when you hit the gas.

Vacuum advance does this by tapping the intake side of the throttle where there is a sudden jump in vacuum when you hit the gas. That jump in vacuum advances the timing.

Vacuum retard does it by tapping the manifold side of the throttle (different position) where there is a sudden drop in vacuum when you hot the gas. The drop in vacuum releases the retard and thereby advances the timing.

With no vacuum advance/retard you lose that sudden timing advance that's key to low speed drivability.

If you connect a vacuum retard port to a vacuum advance distributor, you really screw the pooch. Set your no-vacuum timing to 10 BTDC, then connect the vacuum line and it will advance the timing to 15 BTDC and your engine will race. On a stock B20E you will have trouble getting the idle down below 1000 RPM. And when you hit the gas, instead of the timing jumping forward, it will jump back - just the opposite of what you want. This is what happens when you put a 123 in a B20B or B20E. All they need to do to fix it is to reprogram those curves to be correct, but they refuse to acknowledge there is a problem.

The only way I got mine to work (stock B20E with D-jet) was to modify the vacuum plumbing on the engine to connect the 123 to an intake vacuum port rather than a manifold port to match their broken vacuum programming. It works much better than leaving the vacuum off completely, but I still want to see 123 fix this.