The carbs on my machine required stripping to the component parts. First job after stripping was to degrease using white spirit. I then immersed the entire body in phosphoric acid (Jenolite) for 5 minutes, any longer and you wont have a carb! Some scrubbing with a fine brass brush may be necessary to remove stubborn/engrained dirt. Rinse away the acid using running water and dry thoroughly.
The float valve and jets were soaked in carb cleaner to dissolve fuel residues and wiped clean. The hinge pin that retains the float assembly and the tang that actuates the float valve should be polished with brass cleaner, this helps to avoid petrol flooding the carburettors. Compressed air is useful to make sure that all the passageways are now clear. Aerosols of compressed air are now available if you don't have access to a compressor. You are now ready to re-assemble. My gaskets & o-rings were no longer serviceable so have these to hand before starting. N.B. The Honda gasket set does not include the two 9.6mm o-rings for the balance pipe.
Known problems:-
Make sure the four inlet manifold brackets are in good shape and do not leak air. Problems here will give poor idle, low vacuums & difficult starting, especially from cold. I tried to repair these with 1 contact adhesive - Failed due to it being soluble with petrol, 2 Epoxy resin - Failed due to its intolerance to high temperatures. In the end I gave in and bought new from Honda.
The float valves are prone to sticking, especially after storage, causing petrol to flood out of the overflows. Before stripping the carbs be patient. Waiting a couple of hours, (with the fuel tap off) can in some cases allow the stale fuel residue to dissolve into the fresh fuel and effect a perfect cure!
I avoid my floats sticking by turning the fuel tap on for a short while twice a week. This keeps the float chambers topped up with fuel, you'll be amazed how quick the fuel evaporates from them.
N.B. Check that the float height is correct also.