Must be a typo, 10 litres is just over 2 gallons, thats nearer 100 mpg.
How's the oil pressure/head gasket issue going?
Well spotted, should have read 21 litres. The oil pressure is now adjusted and I've finally settled at 60psi hot and its no problem. No leaks from the gasket. I'm still amazed at how quiet it is now I've replaced the square cut drops for the helicals and added the second silencer in the centre pipe. I'm now thinking about fitting a radio.