With a carby setup, a return does not become a huge issue as the pump will just slow they flow a little when it reaches a pressure... It's not an issue of the engine not getting enough fuel, without a return line, you have nowhere for the unused fuel to go. This being the case in a EFI setup where fuel flows thru the rail, instead of filling a bowl in the carbys.
Do the solex you are using have a return fitting on them at all?
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