Honda-SOHC

Sometimes wiping the rotor with some alcool is all what it takes to calm things down... temporarily  .

I have no knowledge of any extra GND wire, not separate I mean. There is a thick green wire supposed to connect to the frame where the coils are, but that is part of the harnass.

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The reason to vary idle mixture screws one to another is well established by Honda setup routine though. Theres nothing wrong with doing this.

Effectively, their setup routine specifically tells you to do that on a cylinder by cylinder basis. By turning screw out to go lesser until it fails some firing events tells you where air fuel,parity is for that cylinder. Then it instructs you to turn the screw back in again until you make a 100rpm drop in crank speed.  That sets the individual cylinder to its optimum ..... given the prevailing hardware, fuel used etc.
What this achieves is parity of combustion at the tickover rpm to facilitate smooth running and set the "gain" or slope response for the idle circuit to bring the engine up into running on main jet and needle.
Also,, its the fine detail that people THINK is sole responsibility of carb synchronization routine, which doesn't have the fine resolution to enact this part.
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I wonder if that setup routine was maybe prescribed for twins, where I can understand it can work well. I have my doubts where it concerns our Fours. My CB500 carbs lack acceleration jets and I like to think of the slow jets as auxiliary jets that happen to double as idle jets. Across the pond they still believe in plug chops at idle. From experience I can tell you, it won't work, not on a CB500. Either I have plugs with the ideal color and poor acceleration, or I have a good acceleration and black plugs if I idle too long. Anyway, decades ago, without having read anything on it by Honda, I got the idea myself. In practice it didn't work. Also it is very, very time consuming, I can tell you, as you have to wait at least 20 seconds after each minor adjustment step and there are many steps... I judged the method as typical a theoretical thing from the books. So far I have not seen a video that could convince me. That is: I can't remember I have ever seen it demonstrated on a Four.
If one is lucky to have a 4-4 exhaust, one could try by comparing the sound at the end of each pipe and fine tune the airscrews until each pipe produces the same sound. To avoid the gasses, one could use a rubber hose like a stethoscope. Would be nice if we could arrive at a recording of the right sound for reference. And also which sound indicates a too rich and which sound indicates a too lean setting. I was told experienced professional mechanics, familiar with our models, could do the adjustment by ear.

No and No, blueing is probably single skinned aftermarket headers

Thanks, Bryan. Exhausts are OEM. I never quite understood what causes blueing. A since long deceased racer once told me that when the headers blue, one way or the other, your firing is late. I'd like to learn more on this.

A CB500/550's advance begins at ~ 1150 and ends at 2300~2500 rpm.

You need to check the pivot collar carefully as they wear more than the bushes but are horribly expensive.
The difference in bushes is that early ones had a phenolic thrust and felt washer which you dont use with the shouldered bronze bushes but you do use the steel cupped end washers

Also the collar has been modified on the models I indicated in reply #3 and the steel cupped end washers were abandoned. This to stress once more how important it is that you know what exact model you're dealing with. Always consult either the part lists or CMSNL. The latter cannot be praised enough for providing info on what other models the same part was used, once you have logged in. A great service.

This is the the repro I bought in March for € 55,-, a few euro's more than a rebuild set costs. https://www.fourdeelshop.nl/product/6269547/hoofdremcylinder-enkele-schijf-aftermarket CMSNL has them. Works excellent. BTW, you can replace that nasty black cap by the cap of your original MC.

Thank you, Sir.