Read my plug....

If your fuel contains a lot of aromatics, you will get more soot. You might be looking at the wrong part of the plug to read it. What you need to see, is right down inside the plug. There should be a narrow black ring on the porcelain insulator, right down inside where it meets the metal. In any case, I never use plug readings to set the mid range jetting which is controlled by the needles and needle jets. I only use plug readings to check that my main jets are large enough to stop pistons and valves from burning. On road bikes, and even with race bikes, you probably do not use the main jets as often as you might think.
The heat range of the spark plug determines the combustion temperature at which the black ring on the porcelain appears. So use a hot plug for tuning and a colder one for normal hard riding.
What I normally do is set the needles and needle jets almost lean enough to get a cough when I ride the bike changing up through the gears. But my main jets are always slightly too large. When I reach full throttle, my motor gets a bit of a reprieve. - But that is for racing. Most of my accelerating is done as I am winding the throttle on. I do not whack the throttle wide open and then wait for a response. I use the leanest needles I can get. The taper on the needles compensate for loss of vacuum. But if the taper is too fast, you accelerate slower if you feed the throttle on too quick. And it is easy to do that.
It is the distance that the carbon burns off down the insulator and the fact that your main jets are always slightly too big, which are important You should not burn a piston by being too lean in the midrange. If you are too lean in the midrange, you will usually be aware of it, because the bike becomes a pig to ride.

The bike is rarely ridden full throttle. Mostly 1/4-1/2. So the only real change is the needle clip location. It is costly
to be playing with the slide despite it having much to do with lower speed running. And yes, of course, the idle
air screw.

Most bikes I have owned have had number 3 slides. Once you set the idle screws, it is usually set and forget. The slides only affect the first little bit of throttle opening. Some guys who use methanol fuel, cut the slides right up high because they don't know how to get the needles and needle jets right. If you have to get the cut-away higher, you are already doing something wrong with the other jests.

Onder said:

The bike is rarely ridden full throttle. Mostly 1/4-1/2. So the only real change is the needle clip location. It is costly
to be playing with the slide despite it having much to do with lower speed running. And yes, of course, the idle
air screw.

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Most guys do not try different taper needles. The taper compensates for loss of vacuum as you wind the throttle on. The bigger the port, the more likely you are to need a quicker taper. If you use a taper which is too quick, you lose power, but it might be safer. When racing, you usually end up on full throttle part of the way down every straight Riding on public roads is different.

Riding on public roads is different.

Absolutely positively. We tune our bikes and beef them up to go faster largely because in our youth that is what it was all about. Now it is a waste of time as it is faster and cheaper to just buy a modern bike.

We do want our old bedsteads to run well though and we do try to get them to run reliably. There are so many problem areas on an old bike that sometimes the
effort can be exhausting. Initial design not perfect, manufacture surely imperfect, 50 years in existence doing it no good either.

Onder said:

Riding on public roads is different.

Absolutely positively. We tune our bikes and beef them up to go faster largely because in our youth that is what it was all about. Now it is a waste of time as it is faster and cheaper to just buy a modern bike.

We do want out old bedsteads to run well though and we do try to get them to run reliably. There are so many problem areas on an old bike that sometimes the
effort can be exhausting. Initial design not perfect, manufacture surely imperfect, 50 years in existence doing it no good either.

Click to expand...

Plus modern vehicles have upped our expectations and lowered our tolerance levels, maybe??

EstuaryBoy said:

Plus modern vehicles have upped our expectations and lowered our tolerance levels, maybe??

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Well spoken.

I have a 2020 Harley and 2019 Enfield 500. My Commando feels the most up to date... when it goes!