A header pipe that glows red, especially at idle or soon after starting, means far too much heat is reaching the exhaust. The usual causes are a misfire (unburned fuel burns inside the catalytic converter), a very lean mixture, retarded (late) ignition timing, or a blocked catalytic converter. The K-Light manual warns that faults in the ignition, charging or fuel systems damage the catalyst, and says not to ride with poor ignition and not to run the engine for long with a plug removed to look for a spark. A glowing pipe can set fire to fuel leaks, luggage or dry grass.
Is it safe to ride?
No. Stop the engine at once, away from dry grass, fuel and people. Let it cool fully before touching anything.
Quick checks first
- Do not touch the pipe; it can stay dangerously hot for a long time after stopping.
- Is the engine misfiring or running roughly?
- Is the engine warning light on or flashing?
- Any smell of fuel, or fuel dripping?
Diagnose it step by step
1Is there any fuel leak or fuel smell near the hot pipe?
- Yes: keep away, keep sparks away and let it cool. Fix the leak first: Fuel is leaking or dripping.
- No: go to step 2.
2Was the engine misfiring, or is the warning light flashing?
- Yes: unburned fuel is burning in the exhaust. Read codes with Read engine fault codes (fuel injection) and go to Misfires or stutters when accelerating hard or climbing. Do not ride until fixed.
- No: go to step 3.
3Once cool, read the plug with Read a spark plug. Is it white or blistered?
- Yes: lean mixture. Check for an intake leak with Find an intake air leak and see Engine runs hot and lean, pops and pinks. Carburettor bikes: Clean the carburettor.
- Black and sooty: rich mixture can also overheat the catalyst. Go to Black smoke from the exhaust.
- Normal: go to step 4.
4Is the engine also overheating, losing power or pinking?
- Yes: retarded timing or a blocked exhaust. Ask for Check the ignition timing and check cooling with Check air cooling (fins, airflow, mixture).
- No: go to step 5.
5Did it happen after long idling in hot weather, or after holding high revs on the stand?
- Yes: some colour change can occur in these conditions. Avoid long stationary idling. If it glows again in normal riding, see a workshop.
- No: a workshop should check the catalytic converter for blockage. The K-Light manual says catalyst parts must be original and replaced by a dealer.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Misfire | Rough running, MIL flashing | Read engine fault codes (fuel injection) |
| Lean mixture | White plug, intake leak | Find an intake air leak |
| Rich mixture overheating the catalyst | Black plug | Read a spark plug |
| Retarded ignition timing | Overheating, low power | Check the ignition timing |
| Blocked catalytic converter | Low power, heat, no other fault | Workshop |