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Providing that your Scott isn’t four-stroking/spluttering on hard acceleration, and is generally running well, I would be inclined to leave the carburettor well alone. This modern brew masquerading as petrol seems to be very variable between the suppliers, but I would avoid the ethanol containing grades by using the top grade “Super Unleaded”, etc., or by using Murco petrol, which in most, but not all, parts of the UK, does not contain any ethanol in all grades.
The late Jim Best would often remark, “I like ’em to run a bit rich, ‘cos petrol is cheaper than pistons”. Running the slightest bit weak is very bad for any two-stroke, as they run too hot, which encourages piston seizures. With the Amal carburettor, the main jet size always used to be quoted as 170, for both 498 and 596cc engines, but that was with petrol that was very different to today’s stuff. I think that for a 596 engine a 200 main jet is about right, and for TT reps, Sprint Specials, etc., even 220, especially if using them hard. I’ve never really tried to accurately work out mpg on a Scott, but as thirsty as 35mpg has been mentioned on bikes used for fast road work, and about 60mpg in more gentle road work. I think that the slimline vintage Flyer tank holds about 1 and 3/4 gallons, so yours is probably a bit on the thirsty side, but if running well I would leave things as they are. Hope this helps.