the BS34 carbs description sounds good so far.
One issue may be that the idle srew is set to open the butterfly valves to much.
Try starting with reduced opening / lower idle speed.
You had the ignition rotor apart, which was necessary, for sure. But it is possible to mount it back by 180° turned. You still have ignition sparks as normal, but the timing is perfectly wrong! Have a look at that.
To break off a stud from the clutch base is typically caused when the central nut needs to be opened or closed again, but the wrong tool like a simple metal bar was used to hold the clutch base. A special tool is required to avoid that.
Good luck !