not read all the posts, But my Old R5GTT used to suffer terrible Carb freeze even if the ambient air was sill above freezing (if you ever put petrol on your hand its freezing even when the temp is warm.
If your doing motorway miles its very easy for carb freeze to happen, if its doing it around town its no doubt a adjustment or a blocked jet or enrichment/gasket/vacuum leak.
there is a great Haynes manual on Carbs i recomend picking it up , covers nearly all European carbs from late 1970s to the phase out