UK models don't have spark arrestor screens, so yes I did check that in a sense. Also I had the muffler off, and examined the exhaust port - only minimal carbon, which I scraped off anyway.
These carbs are not available on Ebay UK at the moment, and US sellers won't ship to UK.
Here is the link showing how much mainstream suppliers are asking in the UK.
There is 20% VAT on top of the price shown. So all told nudging $200 US dollars for a freaking carb! If you can find me a US seller who'll ship to Uk for sensible money I'd appreciate the info.