Ok, forget it, and sorry for this help thread...my bad
In the JU88, the fuel cocks are completely blinded by pilot's seat!
It's impossible to find them without watching this video on youtube:
For COD noobs like me, would be useful to have each ingame plane video starting procedure as sticky somewhere on forum...(hoping it doesn't exist already - couldn't find them anyway)
Well, if a moderator wants to delete my stupid help thread