Update, hopefully with an interesting observation.
The duct tape fell off after a couple of mows (of course) and I took off the cowl and attacked the edge nearest the intake tube with Mr Dremel and epoxied the hole.
This mower has always had a habit of kicking back unless given a good fast tug on the rope, so much so that I learned to put on a glove rather than get hurt fingers when the handle tears out of my bare hand.
I haven't bothered pulling off the flywheel to see why/if its too advanced.
The coil needs to come off to remove the intake tube. Usually I use a business card to set the gap but this time just used a bit of slightly thicker cardboard cut from a box of biscuits.
The kickback has disappeared - ? due to the thicker cardboard?
Also rubbed a bit of O-ring grease around where the intake tube enters the carbie. The motor is now "purrfect" right through from very slow idle to full chat.
