2006 klx250s i had just bought. 5200 miles and very, very clean. First bike i has ever bought actually. I bought it as an investment/starting bike from an auction because i had never ridden before.
When i bought it the bike would not turn over. After a battery replacement, carb rebuild, and new plug the bike runs and drives fantastic. However, during the first drive (3 or 4 minutes) the exhaust pipe coming out of the head was red hot. After just removing the muffler, and running it for the same amount of time it was normal.
From my search it sounds like my bike may be running lean? I have not checked the plug yet with the muffler on it and running.
https://www.motosport.com/all-*****-...or-rebuild-kit
This is the rebuild kit i had used, everything was replaced except for the main jet. I assume that kit contains the factory jet sizes.
My question is, do i choose the wrong jets? or could it be the muffler is plugged and not letting enough air through. If so, ill order an FMF slip on. If so, would i need to adjust my jets for that also?

 

Did you leave the choke on?

 

From the factory, KLX's are jetted pretty lean to help pass emissions. They also have other pollution control mechanisms like a fresh air induction system that lets clean air into the exhaust stream as it leaves the cylinder head. One side affect of the lean getting and air induction system is really hot exhaust gas. So to answer your question, the jets aren't "wrong" in a stock bike sense, but different jetting would give you cooler exhaust and more importantly a better running bike. Also, the air induction system can be disabled and removed to further reduce exhaust temps and remove excess crap bolted around the engine.

I highly doubt your stock exhaust is plugged. It is restrictive (and quiet) but that shouldn't exacerbate the hot exhaust problem. If you order an FMF (or any aftermarket muffler), you'll definitely need to rejet.

 

If you let the bike run while sitting still, the header will start to glow, no cooling air and the exhaust inside is up to 1300 degrees F per MXA magazine in an article on cooling..



So if you let the bike sit there and idle the head pipe will eventually start to glow after a few minutes. If jetting is lean it will get hotter faster. But with single wall exhaust header pipes they glow and will change color due to heat. The reason most street bikes have double wall pipe or shields that cover up the pipes.

Jet your bike properly, don't let it sit and idle for more than a minute or two, and ignore the pipe if it does glow. The only way it can hurt is if you touch it.

 

Thank you all for your quick replies. After i put the stock exhaust back on, and found a loose ground wire, I haven't had any issues with the exhaust. No glowing whatsoever and the bike performs greatly. Thank you all for the advice!

 

Let it sit and idle for about 5 minutes in the dark...

 

Yes we did. About 5-8 minutes. It was maybe at the very top, (dark red) temperature level of the graph you posted. But NOTHING close to what is was before

 

If it was that bad it probably needed jetted. I let my old SR500 idle once for about 5-10 minutes in 28 degree weather and it was glowing bright orange about 10" along the head pipe. Blued the chrome. Within 1/2 block of riding the glow was gone. It was a bit lean, but every bike you see with blued chrome or colorful looking stainless head pipes, got hot enough to glow.

It really isn't unusual considering the temperature of exhaust gasses. Do a search on "glowing motorcycle exhaust" and see what pops up. One was a picture of Ryan Villipoto on the starting line for a motocross race. If there is one bike that is jetted in right it will be a factory motocross bike. So rest easy. Here is Villipoto: