Ehm, the images show the plane before/after the staging. What do you mean by my setup exactly? Its a very small plane and only 4 parts are really relevant, so it should be easy to recreate. Reactor(Pebble bed)->Nozzle->Decoupler->Turbojet The idea is to use the turbojet as long as you are in the atmosphere, then decouple it and use the nozzle when u have to use fuel. Noticed two more interesting facts, 1.If i save/reload after decoupling, the nozzle works fine. 2. If i wait untill im ~20 thousand meters and then decouple, the nozzle gets some thrust but not the full amount. Save/reload also fixes this.