Is A Glowing Red Head Pipe Okay?

Is a red-hot glowing head pipe on your 4-stroke dirt bike “Okay”? No. Is it “normal?” Yes. Is there a way to fix it? Yes, there’s more than one possible solution, although there is one that stands out the most. If the head-pipe is red, that means the engine is getting too hot and needs more cooling. You may not need any parts to fix this though; let me explain…

Head Pipe Glowing Red Hot

What Causes A Dirt Bike Head Pipe To Glow Red?

The most common causes of a dirt bike head pipe glowing red are:

  • Jetting too lean
  • EFI too lean
  • Idling too long
  • dirty carb
  • Engine is not getting properly cooled

Ride It

There are two ways a 4-stroke dirt bike “cools”. Both of them require riding the bike, so don’t think you can stop and wait to let it cool down. In fact, you want to do just the opposite. First of all, riding the bike gives it air-flow through the radiators (If it’s liquid-cooled), naturally.

So if you’re standing still, the cooling system isn’t going to do a whole lot. This is the most common issue for beginning riders and trail riders that do tight single track. The more you stay moving the better.

Head pipe getting red hot from sitting idling

Gas Cools It

The next possible solution is similar to the first, but in a different way. You now know that riding at higher speeds will reduce the chances of overheating because radiators need air-flow. Gas is the other cooling part. The more gas going through the cylinder head and combustion chamber, the more it will keep it cool, to an extent.

Like before, if you’re sitting with the bike idling, it’s not getting enough gas to burn and keep cool, even if your jetting may be correct (although, lean jetting can also cause overheating problems).

A lower-performance trail bike should not have a glowing head pipe from idling. If that is the case, then the jetting is too lean, or the EFI is too lean and needs to be richer. This can be done with a bigger pilot jet for a carburetor, or richening the EFI system with a fuel programmer.

Valves Wear Quicker With Heat

It’s not necessarily the entire engine that overheats from a lack of gas. It’s the valves that start to heat up and eventually burn out. If you’ve been around 4-stroke motocross bikes at all, you have probably heard the term “Burnt a valve.”

Well, this is one of the main reasons why it happens. The valves just get too hot too many times, causing them to burn up the edge and lose all compression. It’s better than dropping a valve, but still can be a costly repair.

Properly warming up your dirt bike is part of it, which is why I never let my four-strokes idle for very long when I first start them up. How do I know this, you ask? Well, I know of many people that have burnt valves more often than usual, and it wasn’t coincidence. No, it was because they putt around on their bikes.

Not only does riding your bike harder and faster give it more air to cool it down, but it also gives it more gas to keep the valves cool, increasing longevity. You will also have more fun riding faster because you’re passing your buddies that are cruising along.

All in all, a four-stroke motocross bike is made for one thing; to be raced, and raced to its potential. You don’t have to out-ride yourself, and I suggest you don’t. But, the more speed you can get, the better off your dirt bike will be. Quite the contrast compared to most other things, huh?

If your bike is overheating on a regular basis, you probably have bigger problems. Check out my article on Why Is My 4-Stroke Getting So Hot to see if any of those solutions can fix it.

Kelley Fager

I help new riders learn how to safely ride and understand how to tune and fix their dirt bike in their garage.

11 Responses

  1. Matt Dailey says:

    very helpfull

  2. Dan says:

    So I’ve checked the Jet settings, fuel screw rotations tested, fluids are ALL new, filter too, but I start the bike and still get a cherry pipe in 20 seconds.

  3. Shaun says:

    I’ve got a 2019 yz 85 and today i just got done riding I noticed the head pipe was glowing red like it was super hot is this normal and should I be worried about anything?

  4. Eben Grobbelaar says:

    I had this problem on my 510 Husky last week, outlet bend on the exhaust getting red hot within 2 minutes, bike not running smooth, requires choke to keep running, fuel running from carburator overflow. Thought sticky valve problem but found o-ring on seat of carburator float needle and seat failed and fuel bypassing seat, running free fuel to engine, causes rich fuel mix and after-burning in exhaust.
    PS if bike is running without airflow through radiator the whole engine will heat up and not only exhaust. Guess rich and lean mix problems can cause the exhaust heating. Hope this helps.

  5. Caden says:

    I have a 2014 crf150r and the header got cherry red.I read this and should I just let it idle for a little and then go ride and it shouldn’t be glowing what do I do?

    • Hey Caden, any 4 stroke race bike head pipe will start glowing red if you let it idle too long. It needs airflow to cool the engine down. The jetting could also be on the lean side. Has it always done this?

  6. Julie says:

    Very insightful, thank you!
    I have an 06 yz450f. We just rebuilt the top end and during first fire the header started glowing within 10-15 seconds. The carb was leaking fuel so it was definitely running lean. We are obviously going to pull the carb and button it up but considering how fast the pipe started glowing, do you think there could be another factor aside from just the lack of fuel?

    • Hard to say. Lacking fuel would definitely cause it to run hot that quickly. I would solve that and then see what happens. One thing at a time so you know what causes or fixes an issue.

  7. Jeff says:

    I just bought a 2021 Honda CRF 450RL. I started it up at the dealership thinking I’d let it warm up a bit before loading it in the trailer. The dealer reached over and turned it off saying that I don’t want to let it idle because the exhaust will get red hot. Got it home and putted around the block a couple times in the cold. When I pulled into the garage I left it running for a minute to do a walk around and noticed the header begin glowing read. Brought the TPMS up just a couple hundred and watched the red glow extend down the pipe almost to the seat in just a few seconds. This sure doesn’t seem right on a brand new $10000 bike.

    • The CRF450L is the street legal version, so the fuel injection system is probably mapped to run lean to meet EPA emission regulations. Lean = hotter running engine, so I’m not surprised that your brand new bike is running hot when idling.
      The other problem is simply that a liquid cooled bike needs air flowing past the radiators to cool it down. Even if the EFI is rich enough it will eventually get hot if you just let it sit and idle too long. This results in the glowing head pipe you saw. You can either get it re-mapped, or just ride it and don’t let it idle too long.

Leave a Reply

Your email address will not be published. Required fields are marked *