yes, I'm wrong, I mis read the mail from Paul Bailey:
"The first 40 or so V5 engines were fitted with our MK1 decompressor, this was redesigned (MK2) and has been fitted to all engines since (about 150 engines) The problem reported was with a MK1 system not the one fitted to your engine. "
Morgy, I did follow all your advice, and it did help. (I know nothing about paramotor engines )