Thank for the replies, lots more than what I was expected.
First item: I just looked and the tag on the mower says 25:1, but I was going by the instructions on the oil that say 50:1, so 80ml of 2 stroke oil per 4L of standard unleaded petrol, current brand is Bynorm. I have been doing that forever. If that is too lean then it could be the reason for the scoring? I'll see if I can post a pic of the piston, I took a photo through the exhaust outlet, and also felt through the hole and it was not smooth.
Fuel flow: I disconnected the tube from the carby and opened the tap. I got a steady flow, not a strong jet like a hose but more than a dribble so I figured that would be enough.
I'll also start looking for a replacement motor. I called a local shop yesterday and he said he threw out a couple a few weeks ago as no-one wants the 2-strokes any more. How to I know what is the right crankshaft and blade boss?
Norm - I will PM you.
