blue pipes

[unblind]

I recently installed Marks exhaust and DJ stage seven kit. The rear two pipes are VERY blue .
Set floats dry on bench, running fairly well, some popping so still playing with it but -- why are the rear two pipes SO blue while the front two look fine just turning light gold. :confused2: Too lean only on rear cylinders?
BTW all plugs look the same, barely tan

Any advice appreciated.

 

[ninjaneer]

can't take credit for these words nor can i vouch for the veracity:


Indiana Randy of Fort Wayne, Indiana says

Gold and blue pipes result because the exhaust is running too hot. There are three reasons for this. The first, most common reason, is that the bike is running lean. A lean mixture causes exhaust temperature to rise very sharply. A slightly rich mix WILL NOT CAUSE BLUED OR YELLOWED PIPES.

However, a *VERY* rich mix can result in an extreme case of bluing. This happens when the mix is not completely burned in the combustion chamber, (either due to a too rich mix, malfunctioning coil, burned valve, improper timing, or whatnot) and rather ignites INSIDE THE EXHAUST. This can result in an exhaust pipe that GLOWS RED while the bike is running. Only in this extreme case can a too-rich mixture cause bluing.

The common myth that blue is lean and gold is rich (or the reverse) is just that. A myth.

Third, long periods of idle can cause pipes to blue because there isn't any airflow to blow off the heat. (Some people let their bikes idle WAY too long upon start up before they take off)

 

[MaxMidnight]

Another point to consider is that the front pipes benefit from cool air whereas the rears are shielded by the motor.

It seems reasonable that they would run hotter.

 

[SpecOps13]

Way way back, Yamaha tried different jetting in the rear carbs. They gave it up though.... My 94 runs a tad lean, my pipes are gold in some places and blue in some other areas close to the exhaust valves. I'm fine with that... A/F is almost a flatline all the way, 14:1 Ratio..