Blenheim Mk IV start up ?

[Plt Off JRB Meaker]

Ok I'm making a real mess of this,here's my start up procedure please tell me where I'm going wrong.

1:Turn on fuel cocks x3
2:Open radiators x2
3:Turn on carburettor heats x2
4:Switch on magnetos x4
5:Switch mixture controls to half way
6:Switch throttles up to about 15-20%
7:press shift + 1 to select engine 1,press engine start button
8:press shift + 2 to select engine 2,press engine start button

At this stage the engines fire up but die,this is doing my head in please help.Thanks