Discolored Pipes - Honda Rebel Forum
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post #1 of 29 Old 12-23-2012, 04:53 AM Thread Starter
 
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Discolored Pipes

I see every now and then bikes with discolored Pipes, all blues, purple, and such. And I'm wondering is this just that happens to some bike over time, or perhaps a sign that it has been over heated?

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post #2 of 29 Old 12-23-2012, 07:02 AM
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Chrome (and stainless) will discolor with heat.
They start turning gold, then blue. The deeper the blue, the higher the heat they have been exposed to.

Some exhaust pipe will discolor slightly when run at normal temperature. Many of the aftermarket exhausts for the Rebel are of such a construction.
OE Rebel pipes are a double wall with triple wall up near the head, and as such shouldn't discolor unless exhaust temps are too high.
High exhaust temperature usually indicates a lean condition.

My OE pipes have a slight bluing due to times of running full open for many hours at a time. They mainly turned on a trip to Toronto because of four hours on running flat out then hitting a chilly heavy rain. You can see the slight tinge of blue when looking closely.




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post #3 of 29 Old 12-23-2012, 08:25 PM Thread Starter
 
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Thank you for the explanation BG.

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post #4 of 29 Old 01-04-2013, 10:37 PM
 
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Our used 2002 Rebel with just 2000 miles had discolored pipes on it when we bought it. It worried me but we bought it anyway. The previous owner said when he took the MSF course, the instructor told the students to leave the choke on until they saw black smoke coming out the pipes. The owners manual says to NOT leave the choke on longer than necessary as it will discolor the pipes and cause some other problems. Must be unburned fuel passing through the engine and burning in pipes causing excessive heat. Can't be good for the engine. Even though the oil had been changed shortly before we bought it, it was black from the soot. Plugs were black and fouled too. So the moral of the story is get that choke turned off ASAP.

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post #5 of 29 Old 01-05-2013, 01:24 AM
 
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Actually, a rich mixture would run cooler than a lean mixture.
In a rich mixture, the excess fuel absorbs more of the heat, resulting in a cooler exhaust temperature.
Sounds like your bike had been running in an excessive lean condition for quite some time to discolor the pipes, especially if they are a stock exhaust, which has double and triple walled tubing construction.
You would need a very high temperature to discolor the multi walled tubing vs. an after market exhaust, which are usually just single walled tubing.
I think the PO was being misleading about the color of the pipes if he was the original owner of the bike.
I would bet the bike was ridden hard at a very lean condition for quite awhile to show those types of symptoms.

Loud pipes save lives...Nah, they just sound cool.

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post #6 of 29 Old 01-05-2013, 10:11 AM
 
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The "air induction" being used on newer motorcycles (with single wall pipes) causes the extra heat that contributes to the rapid bluing of the pipes.(also increases the lean factor). This is also why owners delete this system.

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post #7 of 29 Old 01-05-2013, 03:41 PM
 
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Quote:
Originally Posted by Superglide;207581.
The previous owner said when he took the MSF course, the instructor told the students to leave the choke on until they saw black smoke coming out the pipes.
If true, this was very poor advice. When black smoke is coming out of the pipes, you have black soot deposits on the plugs and the engine is running really poorly. My advice would be to leave the choke on until the engine will take throttle and make power normally. Then get it off.

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post #8 of 29 Old 01-05-2013, 11:16 PM
 
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I am pretty sure the owners manual says that leaving the choke on too long will discolor the pipes. Certainly a lean condition will run hot and can hole a piston. There used lots of blue pipes on bikes with 4 into 1 exhausts that had not been rejetted. The guy that had my bike inherited it from his father who traded down to a scooter because the Rebel was too much for him and the son said he had never exceeded 45 mph - he had just taken the MSF course. He had never been out on the highway.

So here is what the manual says in the section on starting the bike. After the part about leaving the choke on until it runs smoothly:

NOTICE Extended use of the choke may impair piston and cylinder wall lubrication and damage the engine.
Snapping the throttle or fast idleing for more than about 5 minutes at normal air temperatures may cause exhaust pipe discoloration.

This follows the section on how to use the choke so I assume the fast idleing they reference is caused by the choke.

So I am convinced that this is why our pipes are blue and it certainly wasn't a lean condition. Now, if snapping the throttle and maintiaining
a fast idle with the choke OFF caused the pipes to discolor, any of us stuck in traffic on a hot day would also have blue pipes.

So I guess we can continue the discussion.

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post #9 of 29 Old 01-07-2013, 01:54 AM
 
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This is the wording from my manual for my 2009 Rebel...
--------------------------------------------------------------------------

Starting Procedure

To restart a warm engine, follow the procedure for High Air Temperature.

Normal Air Temperature 10-35 degrees C (50-95 degrees F)

1. Pull the choke lever back all the way to fully ON, if the engine is cold.

2. Start the engine, leaving the throttle closed.

Do not open the throttle when starting the engine with the choke on. This will lean the mixture, resulting in hard starting.

3. Immediately after the engine starts, operate the choke lever to keep fast idle.

4. About a half minute after the engine starts, push the choke lever forward all the way to fully OFF.

5. If idling is unstable, open the throttle slightly.

High Air Temperature 35 degrees C (95 degrees F)
1. Do not use the choke.
2. Open the throttle slightly.
3. Start the engine.

Low Air Temperature 10 degrees C (50 degrees F) or below
1. Follow steps 1-2 under Normal Air Temperature.
2. When engine rpm begins to pick up, operate the choke lever to keep fast idle.
3. Continue warming up the engine until it runs smoothly and responds to the throttle when the choke lever is at fully OFF.

NOTICE
Extended use of the choke may impair piston and cylinder wall lubrication and damage the engine.
-------------------------------------------------------------------------

So according to these instructions, using the choke while riding the bike will cause a LEAN condition, which is bad for the engine and will overheat and blue the pipes.
Note that it does not say to ride the bike with the choke on in any circumstance. It should be off and the engine should be stable before you start out on your ride.
Therefore running the engine until black smoke comes out the pipes is bad advice from an uninformed individual....causing possible engine damage too.

Loud pipes save lives...Nah, they just sound cool.

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post #10 of 29 Old 01-07-2013, 01:56 AM
 
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Quote:
Originally Posted by Sr.MailMan View Post
The "air induction" being used on newer motorcycles (with single wall pipes) causes the extra heat that contributes to the rapid bluing of the pipes.(also increases the lean factor). This is also why owners delete this system.
The Rebel does not use single wall tubing in the OEM exhaust systems.

Loud pipes save lives...Nah, they just sound cool.

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2012 Harley Davidson Sportster XL1200 Custom.
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