After finally getting lucky and picking up a genuine 1975 cb550F supersport fuel tap for my 12/74 cb550F I discovered to my dismay that it's a larger diameter than the threads on the 77/78 cb550FourK tank that I bought. (Yes I should have measured before buying it!) I surmise that the fuel outlet is a smaller diameter on the later model tanks. Also the filler flap is different having a bracket spotwelded on the underside that prevents the flap from closing unless the fuel cap is done up. (The older models fuel cap's hinged handle is replaced with a traditional ridge on later model caps.) As this will still end up looking like the right tank for my supersport project I decided I will still use it.
So I went out and rummaged around in my garden shed and pulled the fuel tap off what looks to be an early cb250 tank that I found at the tip. It has twin outlets and a sediment bowl and low and behold it fits my 550K tank perfectly!
Now my only concern is whether it might be too long and hit the engine! -I will update when I find out.
