No, no..nothing that exotic....yet.
The K0 and K1 engines all used spark advancers that had either 40 degrees or 36 degrees of advance. By late 1970, these were dropped to 26 degrees, although occasionally I would see one come by that had the earlier units in them (when doing someone's tuneups, usually). All of the glass-pack-muffler equipped 750s I remember had these longer advance units in them. As soon as the K2 came out, with its 5-chamber mufflers, the advance dropped to 26 degree units and stayed there for the rest of the CB750K series (K6).
One of my "hop ups" is to widen the stops on the advancers to 36 degrees if you have a stock cam, then run premium gas. Often, this makes the spark plugs show up whiter: in the 1969-1970 era the D8E spark plug was the stock plug. When the advancers dropped back, Honda began using the D8ES, which has a wider heat range and can take extra heat. When the advancers dropped to 26 degrees, Honda used the D8ES-L plug, which was a D8E with an extended electrode that made it sort of a "D7.5E" heat range, a little hotter than the D8ES. At this same time, the ND X24ES-U/X22ES-U series appeared: these had the extended tip like the D8ES-L and a marketing gimmick of a U-shaped ground electrode to set them apart in the stores...but I digress...the point here is: making more heat earlier in the RPM range improves midrange torque, and it can be tailored with plugs of slightly different heat ranges.
The 40 degree units were found in the K0 only, in my experience, and not even in all of them. In those with a 40-degree advancer, you would find the cam had more duration and it started earlier in the intake valve, with the same exhaust specs. This makes for more high-RPM horses: the glass-pack mufflers breathed out easier than the later models and Honda eased off the cam intake cycle and spark advance angle to reduce heat.
Today, I cannot even find the D8ES-L or the X22ES-U or X24ES-U plugs: they have been replaced with "broad range" units like the D8EA. It's too bad, really, because I notice the extra missing pony or two. I had to lean out the jetting to run with these, so they will stay clean. I ran 105 mains and 24mm floats for years with the older plugs: I have to run 26mm floats and 100 mains with the new ones or the plugs will foul in 1 tank of gas.
