It sounds as though the carb is 'dumping'. This means that the fuel is just being pushed into the engine without being metered through the jets.
A frequent cause of this is a small particle jammed in the jet keeping the needle from seating. This is why the extra fuel filter is legal in FB under MSA rules.
747 is a semi synthetic oil, based on castor. Castor can create a varnish that can also lift the needle.
Have you done a pressure test on the carb?
Rebuilding the carb after every race meeting should not be necessary, the engine isn't that sensitive, but if you are racing on it and have been putting unfiltered fuel through the engine, then obviously frequent cleaning can stop the muck accumulating.
There was a spell a couple of years ago when mucky petrol caused a lot of carbs tro go down, which waswhen the extra filter was introduced.
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