what would cause a glowing header

[steve181]

motor is a yz250f

its been getting colder out, would jetting cause the header to to glow orange?

[Iliketogofast]

Yes, lean conditions cause exhaust gas temps (and other internal temps for that matter) to rise. When the atmospheric temperature comes down, the density of the air increases and vice versa. What this means simply is that when the temperature goes up, the bike would need to be jetted leaner and in cold conditions it would need to be jetted fatter. For a properly jetted bike, temperature changes don't make a big enough change in air density to have a huge effect on jetting, but if your bike was already lean, this would make it way lean, and cause your red hot header.

Check your plug, white is lean, black is rich, tan is good. Lean conditions can cause damage, don't just ignore it.

[450rJam]

cold temps can require fatter jetting, alot of aftermarket pipes are light weight and thinner than stock header so it glows easier

some glow is normal on alot of atv's
(really evident at night)

[mattonln]

some glow is normal on all new 4 stroke's because they all come from the factory jetted lean for emissions reasons. if the bike is not popping on decel or hesitating I wouldn't worry too much about but like he said check your plug. white residue equals lean which could lead to detonation which will cause topend failure. stock exhaust Im guessing? oh and another reason might be because its a yamaha ;) lol

[tayyo789]

Are you just sitting still and running it? Or are you out riding? When you are sitting in a garage or just not moving there could be something as simple as not enough air flow to cool the pipe down. I experienced this with my rebuild a few years ago

[atv fan 28]

i remember one time i washed my 450R which had a HRC kit and forgot to remove the lid after i got done. i started it up and with in a couple minutes the header was glowing!!!