CB750 k0 need exhaust check

[dannycantley]

Hi, I just test drove my K0 for 30 miles for the first time. When I checked again, I noticed that the exhaust pipes 2 and 3 were not brown, it looks like the bike is running lean, but the bike runs fine.

Is that normal? Thanks

[K2-K6]

Welcome to the forum.

It would be useful to also check the plug colours in getting more information in making assessment.

They can be set rightly or wrongly to make the combustion show a little different from one cylinder to another.

Worthwhile to check plugs before going further, 30 miles should be enough to at least show a competent burn characteristic and overall picture.

[McCabe-Thiele (Ted)]

I've never taken a lot of notice of exhaust pipe colour as a reliable guide for air cooled 4 cylinders.

The outer 1&4 will generally  get more cooling than 2&3.

[Bryanj]

If they are Honda pipes they shouldnt discolour anyway as they are double skinned

[Nurse Julie]

Agree with Bryan. If they are double skinned chrome , like Honda OEM or, 300/341 aftermarket double skinned, the downpipes should not discolour. If they have gone brown, the bike is running very, very lean, ie, far too hot.
If they are aftermarket single skinned Stainless Steel, they will discolour at any temperature

[Nurse Julie]

I've never taken a lot of notice of exhaust pipe colour as a reliable guide for air cooled 4 cylinders.

The outer 1&4 will generally  get more cooling than 2&3.

Discolouration on double skinned downpipes is a clear indicator that something isn't correct Ted and should not be ignored. Yes, if the pipes are 50 years old and the bike has had a life, slight discolouration is expected.

[K2-K6]

Could be wrong, but initially thought they meant the exhaust exit pipe to judge mixture and burn.

[McCabe-Thiele (Ted)]

I've never taken a lot of notice of exhaust pipe colour as a reliable guide for air cooled 4 cylinders.

The outer 1&4 will generally  get more cooling than 2&3.

Discolouration on double skinned downpipes is a clear indicator that something isn't correct Ted and should not be ignored. Yes, if the pipes are 50 years old and the bike has had a life, slight discolouration is expected.

The word downpipe was not used by Danny,  I guessed it was the end of the exhaust pipe colour from a 20 mile run that was being referred to as brown as opposed to black or grey. I thought it odd as aside from rust brown is a new shade to me for exhaust systems. i.e.tail pipe.  I've seen nice blued single skinned front pipes never a brown one though unless it was rust.

I agree with Nigel the plug colours  are a more reliable than the shade of a double skinned front pipes.

[Nurse Julie]

True, Danny didn't mention down pipes, that was an assumption. But I've never seen brown silencers either 🤔🤔🤔

[McCabe-Thiele (Ted)]

True, Danny didn't mention down pipes, that was an assumption. But I've never seen brown silencers either 🤔🤔🤔

Oddly enough I have - it was a blown head gasket on a water cooled engine - more like rusty water!

If he had mentioned 1 & 4 were blue that would have been a good clue.