Topic: exhaust pipes

[Serge]

Hello, the exhaust pipes on my bike have a blue color, apparently from Ni oxidation on heating...  (it is on the parts which are closest to the engine). I have heard several opinions on this:

1. It is OK and go like this on every bike after a while...
2. Engine runs rich (some fuel still burns in the exhaust)
3. Engine is overheating (might run lean)

What color exhaust pipes on your bike  ?  - serge

[Tim.]

What brand of pipes, size of engine etc.?

[Serge]

What brand of pipes, size of engine etc.?

it is 750f 1978. Pipes 4-in-1 stock, I guess...

[Tim.]

I'd say they shouldn't blue under normal circumstances.  I have a 1976 CB550F with stock header/muffler and no discoloration after 30,000 miles.

When did you last rebuild/tune/synch your carbs, check your plugs etc?  Do you know when the discoloration took place?

[Serge]

Thanks for the reply. I have the bike only for couple weeks and this is my first one.. I changed the plugs so far and the insulator on the new ones looks rather white and engine gets pretty hot but I do not know how hot is normal... 

[eldar]

Well too much heat is what causes the pipes to blue. WHERE they are bluing is the issue. IF it is right up where they connect to the engine, I would not worry too much, remember our 78s are made to run richer because of emissions regulations. This regulation did not start till 1977. So tintins bike is not subject to this. It is common to get a SMALL amount of bluing at teh engine/header joints. If you get bluing elsewhere, then you are way too lean and need to dial in more fuel in your idle mix.

[cub]

What color exhaust pipes on your bike  ?  - serge

My 4-1 system has a nice rusty color......

[Gordon]

remember our 78s are made to run richer because of emissions regulations.

Someone correct me if I'm wrong here, but weren't the later models made to run leaner due to emissions regulations rather than richer?

[Dirk Laguna]

on my 74, I put on the Mac 4-4 drags....before I installed them, I sprayed almost an entire can of exhaust paint inside, and then ran baffles 1/2 inch from the end.....no bluing yet and didn't re-jet....as the 4-4's are gonna flow alot cooler than a good 4-1 (not that one is better than the other)

if the exhaust system is a newer one...the chrome may not be as good as factory....I still have the OEM 4-4's in my garage attic and there isn't a trace of blue on them....but a friend has a 02 Bonneville and they had started bluing a week after he bought it new

[SteveD CB500F]

Search the archives for "dual skin" as the factory pipes (or some of them) had dual skin headers to stop the blueing.  Aftermarket pipes didn't and went blue (funny that). I can't remember which models had these headers though.

On the Piper 4-1 shown in my avatar (1977) I sprayed VHT 1500 degree clear laquer on the headers after fitting (but before using them) and then baked it on with engine heat!  Worked a treat, especially as we lived by the seaside (Brighton UK) and chrome had an average life expectancy of two weeks!

[Tim.]

eek eek!

[SteveD CB500F]

sticky w

[Tim.]

sticky w

I'm not going to touch that one (really, don't ask, I won't touch it).

[TwoTired]

remember our 78s are made to run richer because of emissions regulations.

Someone correct me if I'm wrong here, but weren't the later models made to run leaner due to emissions regulations rather than richer?

Yes, Gordon, you are correct.  The auto industry was being regulated into producing "lean-burn" engines to reduce unburned hydrocarbons in the exhaust.  Regulations for motorcycles didn't actually happen until the 80's.  But, Honda was attempting to be a leader, and started making changes to their motorcycles in 77 to comply with the lean-burn advocates frequenting the halls of the political legislature.
Lean burn carburated engines tend to run hotter. (Due in part to incomplete atomization of the fuel.)  And, so do the exhaust gasses.

White burn deposits on spark plug insulators, is and indication of lean burn. The 77 and 78 carbs have an idle fuel metering adjustment to achieve the lean burn idle.  Richening these up should help a bit.  But, at cruise throttle settings the idle screws have minimal impact, and raising slide needles may be required to get the plugs into the tan color range.  Then, the exhaust headers shouldn't turn blue.

Also, heat, along with surface contamination can discolor chrome.  The oils and/or waxes in some metal polishes will turn chrome blue at lower temps.  That's why I only use clean 0000 steel wool to clean the chrome headers and exhaust.  I have seen a product, I think it's called Blue-Away, that is supposed to restore slightly blued header chrome.  I have not used it.  And, I don't know by what mechanism it is supposed to work.  But, I'm told, it does help.

[eldar]

I did mean to say leaner. I guess spell check cant compensate for being an idiot and using the wrong word! Well tired, I suppose the heat causes a reaction with air hitting the pipes and this may be part of what causes bluing. I have seen no what to raise the slides in my carbs though. There is only one slot for the clips. One could go up say 5 on the mains and that would allow more fuel. Otherwise a person would have to cut new grooves into the needles and this may cause more harm than anything.