White smoke from crank breather?

Doing some break in on my rebuilt KZ750-4 and when the engine gets up to operating temperature there seems to be white smoke coming from the crankcase breather tube. The only other thing I'm noticing is that when the engine cools down there is some greyish white sludge on the oil filler cap. It starts fine with choke, idles well, and doesn't do anything particularly unusual but as soon as it gets up to temp, the smoke starts to appear. I am truly stumped as to what might be causing this, any ideas?

It's just moisture, it's perfectly fine. If it's been a long time since it's had a long ride, the moisture from the air will condensate in the engine, and that will appear as white sludge when it mixes with the oil. If you start the engine and warm it up, the moisture will start to evaporate and turn into steam and vent out of the crankcase breather.

It sounds like it's got a fair amount of moisture in there - the only real cure is a long ride to keep the engine at running temperature for a long time. It's a pretty common thing to happen if you do a lot of short trips. I ride my bike to work and back - about 10-15 minutes each way, and during winter I get the same symptoms. A 1hr+ ride will sort it out.

I'd guess the oil is contaminated with water or something. Does the breather have tubing to keep water from getting in?
I would drain the oil & inspect it. and do a sniff test to check for gasoline.



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When is the last time you changed the oil? Ed

Just did oil and filter yesterday hoping it would resolve the problem. However, the issue still persists.

Oil get white in contact with water?
Air cooled bike (no water cooling)?

I assume the oil you tapped off was white ish?

If you have replaced oil and filter I would just a ride a long trip, and the problem shall disapear...

Have you removed stock airbox? Water coming into the breather when washing the bike...?

Oil + water = white ish oil...

White smoke from the breather is most commonly blow by gasses. Normal up to a point. Some condensation burning off maybe too but that would be unusual (there shouldn't be water in the crankcase under normal conditions).

Nessism wrote: White smoke from the breather is most commonly blow by gasses. Normal up to a point. Some condensation burning off maybe too but that would be unusual (there shouldn't be water in the crankcase under normal conditions).

gasses from the oil itself?

When I take of the oil filling cap on a car engine, I have never seen white smoke? but it can happens?

Ask for learning and not cavil...

Air fuel mixture that slips past the rings

I'd do a half dozen or so pulls from 4,500 to 7,500 in 4th to get those rings a sealin with a nice slow easy 1/2 mile each time of putting to cool it down..... then a good 20 mile ride should get rid of any remaining moisture.

Been doing runs the past couple of days and the smoke has cleared itself out and the gunk under the filler cap has not returned after I cleaned it off the first time. I don't think the smoke from the breather tube was as dramatic as I was making it out to be, as it was also burning grease/gunk off of the head. In any case, the smoke has cleared and now I continue to dial in idle speed/fine tune the carbs. Thanks all!