Hello expeatfarmer, thank you for your prompt reply. I forgot to take pictures of the machine before removing the engine, but I could find pictures of a complete one on the internet (you see the exhaust pipe I am searching for). With regards the carburettor you see on my picture the small screw missing. Many thanks for your help.

Hi all, I am very happy: I could find three segments, a spark plug and some material to weld an exhaust pipe. I will run in the valves next weekend, and look for the belt of the ventilator. My brother, whose venerable BSA motorbike sometimes needs to be repaired, told me I might find a tickler on Faked.com; let’s wait and see… The mower is nearly operational, after having slept half a century in an old orangery…
See you