Exhaust pipe discoloration

1- Blue means rich

2 - Brown / Black means Lean

3 - What does it mean when your right pipe is bluer than the sky and your left pipe has a tan / brown light coloring?

Background. 1973 850 commando roadster. Broke an exhaust pipe on the way to work (right side). Had to drive it home 30 miles with no exhaust pipe. Made it home, ordered, cut and installed new pipes (no crossover). Took it out today for about a 100 mile run. The bikes a little noisy but rockers are adjusted to the T. Besides that the bike runs amazing. Feels good, great pull, 900 rpm idle (thanks to the forums help earlier this year). 65 mph 4500 rpms.

No noticeable driving difference. Just noisy and mismatched discoloration. Any ideas????

ty!

I've never heard of the blue, rich, brown lean saying.

I did once ask a Norton tuner why one of my pipes was discoloured , not the other one. He said one was probably in the chroming bath a bit longer.

I have seen big differences in pipe discoloration on several of my bikes. I have more pipe coloration on one side than the other on a recent Matchless G12 rebuild and was worried that I was getting differences in gas feed (ie. one side considerably leaner than the other) or even differences in timing from one side to the other. The latter seems impossible given that I am running a wasted spark Boyer ignition on the bike. I have come to the conclusion that the most likely cause is difference in chroming on one side compared to the other and that I will have to live with it.

I have another two bikes that are virtually identical machines (5 years different) but one has exhaust pipes which are quite blue while the other is hardly discolored at all. The exhaust pipes were sourced from different companies (one is Taiwanese and the other British). Guess which one is discolored more? Both bikes are running Boyer ignitions and jetted similarly so I doubt very much the difference is due to fuel mixture or ignition.

I always though blue meant lean and brown meant even leaner.

Lean = hot = pipe discoloration (blueing).

That'd be the other way around - Steel turns brown around 250°C/480°F and blue at 300°C/575°F.

I agree with f-d-m. Blue usually means an over-lean mixture; golden brown means just right to a little lean, depending on your setup. One of mine is fairly blue for then first four inches or so, but I got it that way. The other is starting to turn a light golden brown at the bend.

The pipes on my Speed Triple are golden brown all the way to the O2 sensor - took about 10K miles, and a couple of nice runs around Lake Okeechobee, to achieve. :wink:


Good beer, by the way (Fin Du Monde, from Quebec)!

Blued pipes are a sign that the ignition timing is too far retarded.

I watched a set of Vincent pipes turn from new chrome to bright blue (first ten inches or so) in about three minutes of running with the timing set quite severely retarded . I know it was the timing because I later bought the bike and found the timing was out by a mile. After resetting the timing and removing the blue with an abrasive powder it has not returned.

When the ignition timing is retarded a big part of the combustion explosion ends up occurring in the exhaust header rather than in the head, hence the substantial power loss and extra heat in the header.

Is it possible that you have one cylinder set too far in retard and the other correct? It is easy enough for this too occur with the points setup, not sure what ignition you are running.

boyer ignition.

I am still of the opinion that most of the differences we see in pipe bluing are due to differences in the quality of chroming, not to differences in ignition timing or carb settings. That has certainly been the case on my bikes!!

Worntorn, what was the luster like on the pipes after you polished the blue away? I have been afraid to do that for fear that it will dull the chrome too much where polished. What product did you use for the blue removal?

I used autosol chrome polish. It did take the shine down on that area ever so slightly. From more than about 3 feet away the difference is not visible.

Yellow_Cad said:

Worntorn, what was the luster like on the pipes after you polished the blue away? I have been afraid to do that for fear that it will dull the chrome too much where polished. What product did you use for the blue removal?

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I've used a product called "Blue Away" which does work quite well but also does dull the chrome. I have decided that I'd rather have shiny discolored pipes!!

I'm voting for the discoloration myself as it makes a bike look actually used. I have a friend who cleans his with Q Tips and still loses concours.
I'm glad I'm not the only one who breaks pipes, one of mine let go at the flange last Thursday.
I put it down to the fact that they used the Commando rubbers for the muffler on one side and that let it move a lot.
Rabers in San Jose had a replacement in stock and it is a bit heavier and a better fit.
Sure enough it seems to be coloring differently, good thing I don't care.
Raber said the pipes on my bike were old American made replacements.

blu-away = chrome away. Don't do it!

Cookie said:

I'm voting for the discoloration myself as it makes a bike look actually used.

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I'm with you there. I've never known a well-wrung bike that didn't have some discolouration. Honda went to the lengths of double-skinned pipes in the '70s so I don't think it is something that can be avoided by carb and timing adjustments.

Personally, if the blue on my pipes more or less matches the blue stripe on the tank, I'm happy !