headers temp

[Lorenzo]

Some time after I had this bike, I discovered that #4 spark plug cap was fryed, so I replaced them as a set, + new sparks.
Now after some months, the headers, except #4 are starting to get a yellowish color, while #4 is still the chrome colour of the new headers.

Tere is a spark.

I've measured the headers temps, soon after switching the engine off, and #4 is 30°C/86°F cooler.

I've turned the mixture pilot screw 1/4 of a turn clockwise.

What do you suggest?

Thanks

[Steve]

The yellowing is showing you that it is running to hot, likely due to a lean mixture. Don't lean out #4 to match the others, richen them ALL up to match #4.

#4 was apparently running fine, so turn that screw back out the 1/4 turn that you turned it in, then turn all the others out at least 1/4 turn.

What are the current settings on the screws? Blindly setting the screws to a predetermined setting is only good enough to get the bike running. Once it is running well enough to be off-"choke", turn each screw slowly, listening for the highest idle speed. There will not be much of a difference, so listen careffully. I usually start with screws out three full turns, which is plenty rich. As you turn a screw IN, the speed will go up just a bit, then fall dramatically. At that point, turn the screw back OUT about 1/4 turn and go to the next carb. Note that all the screws will not necessarily end up at the same number of turns out.

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[Lorenzo]

I'll do that.
Thought #4 was too reach.
Temps, for the keens, are 266°C/510.8F( for the lean cylinders) and 233°C/451.4°F (for the correct one).
Thanks

[Lorenzo]

The screws where 1turn from full lock;
Since I did not have a fuel supply rig, I took the headers temps as a reference.
After a couple of attempts, I narrowed the temps (1-2-3 to 4) from 30 to 15degC/59F
Tonight I will try and ballpark it.
Thanks

[Crankthat]

I have used temps to help me find area of problem.
I recently bought a synch and a colortune.

In my limited experience the carbs being out of synch and or uneven flow in your jets from gunk can also change the temps on your headers.

That has led me to the belief that the valves being set correctly and knowing your carbs are clean and in synch would be where to start before diagnose with mixture by header temp.
I would just want to make sure the above is done correctly before setting the mixture by header temps or else you may cause the motor damage.

I am not sure about this but it makes sense to me.
Just a thought.

[Lorenzo]

Valves gap is within specs, checked recently, due to a valve cover gasket issue.
The carbs, might be not spic-and-span, I never opened them, since I had the bike but, will defo be an early fall job.
As far as potential damage to the engine, I am cautious too, through lack of experience, but I would be more weary if I was leaning the mixture instead of enrichen it.
Thanks

[Steve]

One turn out is usually too lean here, but you might have different jetting than what was mandated by our EPA (Environmental Protection Agency). Running rich is better than running lean, and turning those screws OUT will richen the mix. For our jetting, three turns is a good starting point, but most carbs will end up between 2 and 2 1/2 turns out.

.

[Lorenzo]

I am 2 and a 1/2 turns currently.
It might be my own suggestion but, it seems that the engine is more prone to rev.
Before, it had an esithation at around 2000rpm in second gear, I could describe as "hunting".
In the brief commute to work I saw 4000rpm without particular effort, whereas before the engine used to sat at a confortable 3000rpm.
Forgot to mention the plugs colour.
Before tweaking the mixture, 1 to 3 were an hazelnut color, while #4 was sooty but not oily.
Let's see now...

[Lorenzo]

I am 2 and a 1/2 turns currently.
It might be my own suggestion but, it seems that the engine is more prone to rev.
Before, it had an esithation at around 2000rpm in second gear, I could describe as "hunting".
In the brief commute to work I saw 4000rpm without particular effort, whereas before the engine used to sat at a confortable 3000rpm.

[JTGS850GL]

You just described a classic case of the pilot screws being set too lean. Too bad the new headers have begun to yellow. Could have been avoided if you adjusted the carbs in the beginning using the highest idle method. At least you caught it fairly early and avoided significant bluing.

[Lorenzo]

The price you have to pay to ignorance, I guess....