- Joined
- Jun 30, 2012
- Messages
- 13,193
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 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.
Last edited:
