Hello Jan,
Before you go any further renew the sections of rubber fuel line hose, Do not use braided pipe, the rubber inside the braid is not resistant to E10 fuel. We have been forced to use lousy E5 fuel in recent years and it rots the rubber, believe me I know the problem well. Now we are stuck with E10 fuel which is worse and the rubber components in fuel systems cannot withstand it. Hoses rot from the inside and cause them to crack. You may be sucking air through a tiny split or hole but it will be enough to prevent fuel reaching the carburettor.
Clean the carbs out, they may contain bits of rotted rubber.
Use www.advanced fluidsolutions.co.uk - 100% Bio Fuel Hose I.D. 7.3mm Type 2240.0600 or 5.5mm Type 2240. 0400 whichever is appropriate. It is probably twice the cost of that from the usual suppliers, buy a minimum of 1metre, you will need the greater part of it.