Glowing Exhaust Headers

[twigg]

I guess my rear exhaust headers are not supposed to glow, but they were yesterday.

 

The plugs do not show signs of running particularly lean but there is some heat getting back there from somewhere.

 

Currently the carbs are off for a full rebuild, and the front exhaust headers too, to get at the starter. I noticed that one of the headers was very loose in the collector, and this would probably be contributing to the "spitting" back through #1 and #4 carbs. I suspect the butterfly valve seals aren't helping much, the intake boots seem to be sound.

 

Anyway ... I was wondering if anyone else had experienced this. I do know that some exhaust headers, on some bikes do have a "glowing" issue, but I didn't think that the Venture Royale had this ... er ... feature.

 

Any thoughts?

[bongobobny]

Yah, DEFINATELY not normal...

[twigg]

Yah, DEFINATELY not normal...

 

Yeah, I figured.

 

You can't tell if the fronts are glowing too because the headers are double walled.

 

Usual causes of this are:

 

1. You fitted a Formula One engine, and it's normal

 

2. The timing is out

 

3. The engine is running lean

 

Where to start!!!

 

Well I can rule out #1

[bongobobny]

Yah! Timing issue!! Suspect you try your vacuum module near your TCI. Check for voltage input, vacuum line, and voltage output. If you, need a spare one I have one...

[twigg]

Yah! Timing issue!! Suspect you try your vacuum module near your TCI. Check for voltage input, vacuum line, and voltage output. If you, need a spare one I have one...

 

On it ... I'll get back to you.

 

I didn't really suspect the timing because the thing runs so well, right up to the redline.

 

But it doesn't hurt to check.

[dingy]

Are they both glowing?

 

Equally?

 

Are they glowing after hard run or just at idle?

 

If they are doing it at idle, just for something to try, back out the rear mixture screws a turn. Running lean is what causes excess heat. Maybe dumping more fuel in will cool it down.

 

 

Gary

[twigg]

Okay ....

 

A meter across that unit is showing 5.95V

 

It doesn't change when sucking or blowing the vacuum tube. The reading should be 2V.

 

I guess that suggests that the timing is not advancing correctly, and that would fully explain the glowing headers.

 

So yes, it sounds like it needs replacing.

[twigg]

Are they both glowing?

 

Equally?

 

Are they glowing after hard run or just at idle?

 

If they are doing it at idle, just for something to try, back out the rear mixture screws a turn. Running lean is what causes excess heat. Maybe dumping more fuel in will cool it down.

 

 

Gary

 

Yes, they were both looking nice and toasty

 

I suspect that the fault found with the vacuum unit will be the reason ... Fuel still burning when it hits the headers.

[dingy]

Yes, they were both looking nice and toasty

 

I suspect that the fault found with the vacuum unit will be the reason ... Fuel still burning when it hits the headers.

 

The reason a rich condition runs cooler than a lean condition is that the heat is carried away in the exhaust in the form of unburnt fuel molecules.

 

In a lean condition the heat generated is absorbed by the surrounding structure (headers, pipes etc.). The exhaust gases is not as conductive to the transfer of the heat energy.

 

I have no real proof of this, just something I learned at some point.

 

Gary

[twigg]

The reason a rich condition runs cooler than a lean condition is that the heat is carried away in the exhaust in the form of unburnt fuel molecules.

 

In a lean condition the heat generated is absorbed by the surrounding structure (headers, pipes etc.). The exhaust gases is not as conductive to the transfer of the heat energy.

 

I have no real proof of this, just something I learned at some point.

 

Gary

 

I think this is a timing issue.

 

Although the engine appears to be running well, the boost sensor isn't working. This would mean that the ignition timing isn't advancing correctly.

 

When that happens, the fuel is still burning when the exhaust valves open, carrying burning fuel out into the headers.

 

Do it too long and exhaust valves will burn. Plus .. power is being lost as the fuel is beginning to burn too late in the cycle.

 

In a rich condition, some of the fuel remains unburned and is deposited as soot. The burn is cooler and that can be seen on the plug ground electrode.

 

In a lean condition the fuel/air mix is starved, and there is relatively more oxygen available. It burns fast and hot, which can also be seen on the ground electrode of the plug.

 

A cooler plug can carry some of that away, but in the end it will burn valves and pistons.

 

The ideal burn temperature, by the way, is between 850 and 1150 Fahrenheit. The plug heat ranges are designed to keep it in that range.

 

But they cannot compensate for poor timing or a mixture that is too out of whack.