Topic: Smoking breather hose

[timmangan]

I have a 1975 cb550, recently smoke started coming out of the breather hose on top of the engine.

Any ideas what that is about?

Not too long ago I overfilled the bike with too much oil, it was escaping from everywhere so not sure if maybe some is up there and is just burning, causing the smoke.

Any ideas?

[timmangan]

FYI: the smoking was happening before the oil overfill. Just remembered

[TwoTired]

What color is the "smoke".

White is water vapor = normal, until the engine has been at operating temp for 15 minutes or so, at which time the water has all vaporized.  The volume or lingering time is directly related to the surrounding air humidity and dew point.

Blue smoke is oil vapor.

Black smoke is unburned gas or piston ring blow by possibly exacerbated by more choke than necessary.

[kammery]

 What colour are the spark plugs ? Is there any trace of oil fouling ? At times this is caused by compression going past the piston rings or What we call Blow-by .This puts  pressure  into the crankcase .

[Deltarider]

I have a 1975 cb550, recently smoke started coming out of the breather hose on top of the engine.

1. Have you overfilled?
2. Is breather hose blocked somewhere?

[timmangan]

The smoke is white, so water vapor?

It seems to continue after 15mins, it just keeps going.

Should I be worried?

[Black 750K8]

The smoke is white, so water vapor?

It seems to continue after 15mins, it just keeps going.

Should I be worried?

Go a little longer if it is still there after 30 minutes over 4000 rpm then something is wrong.

[TwoTired]

The smoke is white, so water vapor?

yes

It seems to continue after 15mins, it just keeps going.

Should I be worried?
[/quote]
You're not being clear.  15 minutes since initial start when cold, or 15 minutes after the engine reached full operating temperature?
Are you running it stationary?  Or, have you made any freeway runs for a length of time?

Water needs heat to vaporize.  The higher the heat the faster the vaporization process.  Vaporization stops when the water content is all converted.

Have you taken note of the humidity and dew point?

[Lostboy Steve]

Mine did this after I rebuild it. Once the rings settled it went away. Took a few hundred miles or so.

[timmangan]

Sorry twotired, I meant 15mins after a cold start.

I ride about 35mins from home to work, when I get there it still smokes.

I ride in the morning when its cold, in the afternoons when its not so cold, if anything, I think it smokes more in the not so cold temps.

I travel at an average speed of 80mph for 15mins, 65mph for 10mins, 90mph for 10mins.

Don't ask what the speed limits are, im sure they're around that mark

The engine was rebuild a few thousand miles ago by the previous owner.

[MiGhost]

I travel at an average speed of 80mph for 15mins, 65mph for 10mins, 90mph for 10mins.

Didn't know they had the HSV lanes finished already.

Try holding a napkin, or paper towel over the hose end.
If it comes back wet. It will be water vapor. Take a good 1-2 hr ride to make sure the moisture gets cleared out.
If it comes back dry. Take a sniff to see if you smell a burnt oil scent.
If you smell oil. Do a compression test to check the rings.