Red Hot

[400exrider720]

I finally got my quad running right but now I put it in neutral and revved it for about 10 seconds, varying its rpms, and then the headers turned bright red :eek: so what is causing it? I checked the spark plug and it was black so it is running rich. Could it be valve adjustment with the new cam? Please help.

["THE ShoP"]

what kinda headers?

[krt400ex]

my stock pipe does that sometimes when the engine gets real hot. it happens more when im riding in the snow cuz your going at higher RPMs but not moving so fast. it is probably normal, unless it happens all the time and is noticeable during the day. mine is only noticeable at night

[DF400ex]

Usually your headers turn red hot in the winter because you are running too lean. Because the air is colder, it's a lot more dense. Therefor you have more air in your cylinder. You need to bump up your jet size in the cold. I've heard people say that you need to re-jet every 15-20 degree change, or less.

But I don't know why your spark plug is black, it doesn't fit this scenario cuz it should be white if you are running too lean. Are you burning any oil?

[400exrider707]

Well unless its a new plug, it was probably already colored. Also it takes more than 10-15 seconds of run time to get a color reading on a plug. Your main jet could be too rich and your pilot/and needle could be lean.

I would definitely bump up the pilot jet if its getting red that fast.

[400exrider720]

Its an FMF powerbomb header. When I did this it was a nice day outside not night time. I will try getting a new pilot jet. What do you think 42 or 45? The plug was brand new when I did this so it had no coloration before it. I just dont understand what is wrong :confused:.

["THE ShoP"]

try a 42 pilot,an I have the same header. that header is only single wall, everyone that I've seen glows a little red.I just got my jetting strait an it still glows a little can't tell in the day but you could see it a tiny bit at nite

[krt400ex]

Originally posted by 400exrider720
Its an FMF powerbomb header. When I did this it was a nice day outside not night time. I will try getting a new pilot jet. What do you think 42 or 45? The plug was brand new when I did this so it had no coloration before it. I just dont understand what is wrong :confused:.


42 pilot


mine actually glowed from the beginning of the header all the way back to where the header connects to the muffler. scared the crap outa me, but i was in 3rd gear pinned doin about 5 mph in the snow...and it was at night. hasnt happened since

[mod440ex]

you have to remember its an air cooled motor no matter how long it runs for. its going to get hot real fast when your not moving. put a new plug in it and go ride it wide open then kill the engine at full throttle, then check your spark plug and that will tell you what you need to do for jetting.

[400exrider720]

Originally posted by mod440ex
you have to remember its an air cooled motor no matter how long it runs for. its going to get hot real fast when your not moving. put a new plug in it and go ride it wide open then kill the engine at full throttle, then check your spark plug and that will tell you what you need to do for jetting.
I think youre dead on :D . I ran it today and actually drove it and the header didnt glow at all. I am getting a 42 pilot though just for easier starting. Thanks to everyone for all the help.

[redneckrider14]

When i bought my 05 400ex mine was doing the exact same thing. I took it back and they rejetted the carborator and now it is fine. They said that it was gettin to much gas and there was accutally a fire in my head pipe. So try rejetting it.

[400exrider720]

Originally posted by redneckrider14
When i bought my 05 400ex mine was doing the exact same thing. I took it back and they rejetted the carborator and now it is fine. They said that it was gettin to much gas and there was accutally a fire in my head pipe. So try rejetting it.
Are you sying that I should drop the main to like a 168 instead of a 185? I talked to my brother(mechanic) yesterday and he said it was probably getting too much gas making it run hot so this would make sense.

[krt400ex]

Originally posted by 400exrider720
Are you sying that I should drop the main to like a 168 instead of a 185? I talked to my brother(mechanic) yesterday and he said it was probably getting too much gas making it run hot so this would make sense.


no, if the engine is too hot, that would not at all mean a rich condition. if the jetting is right, then look elsewhere