Checking out the Stag Owners Club Forum I soon found exactly the same problem discussed. Fitting new needle valves, checking the level of the floats and fitting a Fuel King Pressure Regulator Filter, were the recommended remedy. I immediately order a carb service kit and the said pressure regulator filter.
As soon as everything arrived I started work by first taking loads of pictures to ensure I remembered where all the hoses and cables attached. The whole assembly was covered in grease and dirt and once I removed it from the inlet manifold I washed all the muck off in petrol. I soon realised there was other things I was going to need, new screws to replace the chewed up ones and stainless fuel hose.
Whilst the carbs were off, I took the opportunity to degrease the inlet manifold and the V of the engine, I also polished the Stromberg top body casing and reassembled with new gaskets, needle valve and diaphragm. Thank God I had taken all of the photos, they were essential to ensure everything connected up correctly. I also replaced the ducting between air filter and top of exhaust manifold with clean shiny aluminium ducting. Finally I fitted the Filter King Regulator and set the pressure with the provided gauge.
I turned on the ignition and with considerable relief, the engine immediately came to life. No more leaks so far. Previously, when I started up I needed to apply full throttle, always a sign of flooded carbs, now I only need to turn the key and she gently rumbles to life, success.
All now ready for the Bank Holiday Weekend.