Dirt bike header red hot (4 stroke)

[Witzkaaa]

I have a problem that I'm not sure how to fix. My brothers bike wasn't starting and when I kicked it, it sounded like the spark plug was going. I replaced that and I got it to start but it would only idle for a second. Once I got it warm by letting it idle for a second each time I kicked it, the idle would fluctuate. It would get high then low then high then low. Then I looked down and saw the header was red hot and I've never seen it happen on both my bikes. I have no idea what it is if someone could send me in the right direction that would be great.

Thanks

[thredbo]

Sounds like an issue in your carb. If it was always running red hot then it's likely your bike was jetted lean, but since it's an issue that's just popped up I reckon you've probably got something blocking or gumming up your jets.

[skorpan777]

The Red glowing exhaust is normal.

The fluctuations on idle I don't know anything  about

[Witzkaaa]

3 hours ago, skorpan777 said:

The Red glowing exhaust is normal.

The fluctuations on idle I don't know anything  about

It can't be normal for my bike, a 2002 yz250f. It's never happened to either of my bikes which both are only a year apart. I also smelt something that wasn't pleasant when I realized the header was red hot.

[MentalGuru]

What make/model bike is the one you're concerned about?

[Witzkaaa]

2001 yz250f

[MentalGuru]

It sounds like a dirty carb to me, but getting the exhaust hot enough to glow is common.  It's really noticeable at night.

I'd start by cleaning the carb completely.

[Witzkaaa]

It sounds like a dirty carb to me, but getting the exhaust hot enough to glow is common.  It's really noticeable at night.
I'd start by cleaning the carb completely.

Ok I will do that and you think that will help with the fluctuating idle?

[MentalGuru]

7 minutes ago, Witzkaaa said:

Ok I will do that and you think that will help with the fluctuating idle?

It should, odds are the carb is dirty and the bike is running lean.  Make sure all the passages and jets are perfectly clean.

[Witzkaaa]

It should, odds are the carb is dirty and the bike is running lean.  Make sure all the passages and jets are perfectly clean.

Will do thanks.

[wesrunner]

Glowing head pipe is normal at idle. Without air moving past it, the pipe will get red very quickly at idle while it warms up. I've heard it has something to do with cold valves not fully seating and allowing combusting fuel to escape the cylinder. All of my YZf's have done this.

Edited April 4, 2017 by wesrunner