I don't go buy quarts or liters. I go by the dip stick. When I refill while doing an oil change I fill to half way between the karks on the dip stack just set on the threads, bike on centerstand and on level ground. Doing this puts the site glass justbelow the upper line.
I know my dipstick is correct because it measures up at what the book says it should. They changed the spec on the oil capacity on the 75 B models, Engine #103747. The measurement on the new dipstick is 5.5 in(140mm) from the bottom of the plastic to the upper mark. The lower mark is 1 in (25mm) below the upper mark. Reccomended oil level is half way between the marks.
I also found that if you screw the dip stick in to check the oil the level reads right at the upper line.
After you fill the engine with oil, start the engine and let it warm up a bit, shut it down , let it set a few minutes and recheck, add a bit if needed. If you have an oil cooler or external oil filter this makes sure oil has everything filled and still has the proper level in the crankcase.