Hate to sound like 'the last word', but here it is on oil capacity of the 750:
Some (not all) of the first K0 bikes have a 3.0 quart tank. These can be identified by removing the tool tray and looking down: if you see clear to the swingarm pivot below, you have one of these rare birds.
The next oil tank, starting in K0, was 3.3 quarts, required 3.5 with filter change. These disappeared with the sandcast bikes, early in the diecast era.
The next oil tank was 3.5 quarts, could take 4.0 with a filter change without blowing over the top of the separator and out the road tube. This remained until K4, when the vacuum canister appeared under the battery box.
The oil tanks on the pre-1976 K bikes with the vacuum canister (K4-K6) are supposed to hold 3.5 quarts, but the filter media in the separator appears to break down in some units, and this lets oil foam or mist get into the vacuum separator and cause the engine to smoke, especially if the rider is not using low-detergent oils. These work better with 3.3 qts. in the tank, 3.5 with filter change.
Then came the mix again: some K6 bikes hold 3.0 in the tank, .2 in the filter. Some have the K5 tank instead, both with the vacuum canister. The oil dipstick tells which one you have: the plastic dipsticks are the lesser size tanks.
Starting with the F0 in the post-1975 era, the tanks are 2.7 quarts, need 3.0 quarts with filter change and crankcase drain. This lesser oil capacity is part of the reason for the short lives in the later engines.
