Thanks MetroMPG allowing me to illustrates my projects.
You will find below the sketch to jump from MA4 -> Last release MA5O.
The potential effect in fuel economy of such a gear ratio change on a Citroen AX :
Same fuel economy graph potential with AX 1,5 D MA5L Gear ratio instead of AX 1.0E MA4.
And finally my project road map overview to reach the 3l/100 km target on my Citroën AX starting from a current 4,9 L/100 with lowering idle speed to 650 rpm.
Thanks to Ecomodder, I earn that with an EOC kill Switch we can decrease fuel consumption. I'am currenty adapting such a switch on my car (very simple on an cabureted engine like mine). I will give you a feed back soon.