Ok, checked petrol cap, hole not blocked, spark plugs NGK B6H S, right side nice light brown colour, left side sooty black, both tapped at slack 25thou. Set to 15thou. Fuel hoses are metal braided which can be seen as the outer covering is cracked and peeling off. Black particles in right side float bowl and lots of soft off-white like gritty salt stuff on bottom of left bowl. Throttle slides are both 4/3. Right carburettor is 274/407R, left is 274AK/4A. Haven't taken carburettors off yet as I'm not sure that I need to to clean them out. Book says slides should be 4/5 and right carburettor is not the standard one, runs fine though so don't think there's a problem there. My thoughts are to clean out and inspect the fuel tank, the fuel hoses seem okay, I pushed a thin wire down each one a few times and there doesn't seem to be any loose bits coming off. Thanks for any advice. Paul