Personally I wouldn't restrict return when the float bowl is full the floats restrict fuel amount and excess returns to tank.
If you've got fuel returning to tank..I put clear pipe on mine so I could see.. then I would strip and clean carbs as a first step and check for any filters po fitted in the line as on tickover engine gets enough fuel to run but under throttle emptys carbs..guess how I know!
If you've got fuel returning to tank..I put clear pipe on mine so I could see.. then I would strip and clean carbs as a first step and check for any filters po fitted in the line as on tickover engine gets enough fuel to run but under throttle emptys carbs..guess how I know!