Topic: smoke and oil from breather tube (cb350f)

[thirdman]

One day while riding home, I started to lose top end power.  By the time I got home, I had lots of smoke and oil spraying out of my breather tube...  What causes this?  I have a 1973 CB350F.  What do I need to do to diagnose the problem?  I figured I would start with a compression test... but what else?

(p.s. I did a search on "breather" and found suggestions that it might be bad rings or a bad valve seal... can anyone confirm?  )

[SteveD CB500F]

Smoke from the breather means you have excess crankcase pressure (usually caused by rings or valve seals as you say)
If you have oil "spraying" out it sounds serious!

Start with a compression test but check valve clearances first.

[thirdman]

I had the full-on James Bond smokescreen and oilslick action.  My rear wheel got coated in oil, and the smoke was thick. 

Worst case, what does this mean?  If rings are toast, does that mean a re-bore?  If it is a valve issue, what all is involved with that?