I've got a CB550 (1974) that I've been rehab'ing. Just got it running on all 4 and managed to run a tank of gas through it this weekend.
Hit reserve on the way home so stopped for gas. It took 3.67 gallons to fill to the same visual spot I was at last fill, and the trip gauge was at 122.
That's 33 MPG.
I didn't do a real plug chop, but when I got home I pulled the plugs and #1 had a smudge of black soot on the electrode and around the metal ring, but insulator white. #2-4 all had very little residue, barely made a mark on my finger, insulators white.
I don't really get much on my fingers if I wipe the inside of the tips on the Emgo's.
So, I'm guessing I'm a bit lean, except on #1.
Now, I was riding spiritedly this tank, whipping it up to 8000 before shifting, went 90+ several times, and probably averaged 70mph the whole tank at ~5000 rpms.
I thought the 550 was supposed to get about 50mpg. I know riding hard will decrease the figure, but by 17mpg?
-K