Is that British gallons or American gallons you refer to when you say you're getting 38-43mpg ? I wouldn't think the oversized main jets will be helping improve economy, might be worth putting the 130's back in and see if that improves things. It's worth checking the condition of the choke plungers as they have a habit of rotting away and letting extra fuel in. A carb balance after any adjustments/changes might also help. 