[fredgold52]

I've seen pipes turn sort of yellow and I've seen them turn deep blue.  Can anyone provide a simple explanation of what the colors mean / what causes them?

Thanks,
Fred

[LotusSevenMan]

I think it depends on the exhaust header manufacturer as to whether it is single or double skinned. Then there is the question of mixture and is it weak or rich or perhaps correct!
The deep blue normally says it is getting very hot so might be running weak or the timing is out. Straw coloured I think is fine (Ie mixture and timing correct).
Lots of variations on a theme here!!!!!
I stand to be corrected so.................

[fredgold52]

I think it depends on the exhaust header manufacturer as to whether it is single or double skinned. Then there is the question of mixture and is it weak or rich or perhaps correct!
The deep blue normally says it is getting very hot so might be running weak or the timing is out. Straw coloured I think is fine (Ie mixture and timing correct).
Lots of variations on a theme here!!!!!
I stand to be corrected so.................

I didn't say which sort of pipe I was asking about.  I meant to ask about our RE pipes which are single layer.

Good to hear about the 'straw' color.  Mine's developing sort of a yellowish hue as I gain miles.

I saw a picture of one of our Classics here.  Great looking bike but the pipe was very discolored and dark blue looking.  That's what made me ask the question.

[Foggy_Auggie]

Mine is 'straw' at about 1700 miles with some very light blue 'rainbow'.  This is just at the first bend out of the head.

My dealer checked the carb float needle and balanced the idle circuits after fixing the sticky throttle problem under warranty.  So my pipe color is assumed normal and I'm not running lean on my box stock Sixty-5.

My plug readings are normal.

[Thumper]

My experience has been: Yellow first, then if they get hot enough, purple. My favorite were the headers on my '72 Yam 650 XS2: Pretty purple, blue and yellow.

Yellow = hot
Purple = real hot

Or as I like to think of it:

yellow = fast
purple = real fast

IOW, "Purple Pipes Mean Fast Bikes"
OK, it makes about as much sense as some other biker stickers...

Kidding aside, the extreme lean running conditions of modern engines sure lends to purple pipes!

Matt

[fredgold52]

OK, so what I'm learning from this so far is, Yellow = Normal, Decently Tuned, Jetting is close.    Blue or Purple = Too Lean, Timing too advanced or too retarded.

Is that close???

[dogbone]

I have always preferred jetting to be a little on the rich side, but usually my pipes blue. I think it happens when I'm stuck in a lot of traffic. I time my engines by ear and exhaust backpressure, It has worked very well over the years.

[Thumper]

OK, so what I'm learning from this so far is, Yellow = Normal, Decently Tuned, Jetting is close.    Blue or Purple = Too Lean, Timing too advanced or too retarded.

Is that close???

Blue and purple don't have to mean too lean. They just mean hot.

All of this depends and several factors, not the least of which is pipe construction. How thick are the walls? Does it have an inner lining?

Unless it has an inner lining most modern, OEM-tuned bikes will have some discoloration - and usually with some purple. They run lean (and hot if air-cooled) - but all within design parameters. No harm no foul.

My bikes with purple pipes have run hot - but some (like the RE) are not running lean - and are running well. Color is not always an indicator of the state of tune.

In past years aftermarket free-flowing header pipes were often thinner than OEM and without a liner, hence the purple discoloration. This is where (in my mind) purple was equated with fast. The fast guys had always popped on a Kerker or SuperTrap as part of their performance upgrade so they were fast and purple! (maybe I should have explained that up front....)

Matt

[cyrusb]

I can tell you that I watched my brand new pipe turn yellow on the FIRST  exhaust stroke after it was installed. Then at idle, by 15 seconds it was blue, went out for a ride and it came back yellow, which is how its been ever since. Go figure. I dint think the colors mean anything about engine state. But probably says something about pipe construction, materials, etc.

[fredgold52]

I agree, Cyrus.  Pipe construction is absolutely a critical part of this equation.  But if we restrict the discussion to the stock RE pipe, that should take some of the variation out of the process.  What you describe sounds wild.  Went yellow right away, then blue and finally yellow again.  I wouldn't have thought it possible. 

Mine is just the lightest yellow, but it really hasn't been exposed to any heat yet.  All my 150 miles have been done in 40 degree F and colder air. 

[cyrusb]

The quality of the chrome job has a lot to do with it also, and  I have noticed that the Indian chrome in general is lousy.  I didn't add that some of the chrome instantly blistered like house paint, also on the first few strokes.

[birdmove]

  Mine doesn't seem to be changing colors yet at 260 miles.

    jon

[prof_stack]

  Mine doesn't seem to be changing colors yet at 260 miles.   jon

Sure, Jon, but wait until you go out for a longer ride when the temperatures are above 50 degrees (can't come too soon for me!).

[Foggy_Auggie]

Very hot summer days and creeping in stop and go traffic will turn the pipe.  Even some slight brown patina on the cylinder head - just like the old BSA and Triumph days.

Thank goodness for synthetic oil!

[birdmove]

    Good point.

    jon