In the early K engines (K0-K6) the valves have something of a 'self-healing' capability. If the lash was set too tightly or too much carbon built onto on a valve face, which then led a wrencher to set the lash at 0.002/3" while it was carboned up, followed by riding it some distance and the carbon falling off the valve face, leaves the valve off its seat. (whew...) Then it has poor compression until someone notices the valve has no clearance, and adjusts it for some, followed by about 100 miles [at speed] when it 'heals' itself.
This activity is actually quite visible on the chamber-face of the valves (as shown on page Appendix D-3 of my book) and the resultant pitting of the valve also shown on that page: to 'fix' it, either a very long ride at high (engine) speeds or else removing and refacing the pits out of the valve sealing face will restore it just fine. That particular engine had 126k miles on it and then got parked for 5 years with no prep, and some rust settled into the faces of a couple of the valves. Previously when this sort of 'leaking' started showing up I just planned a long trip with the bike, which is why the picture at the top of the page shows several 'layers' of carbon burned onto the exhaust valves in different outlines. What I had experienced for many years with this bike is: riding it back & forth less than 10 stop-and-go miles one way to work had a tendency to carbon up the valves, most likely due to the jetting being slightly rich (most K1/2 bikes were). To 'blow it out' I would often take weekend rides at [ahem] higher speeds, just to make sure the high end of the speedo still worked OK, and it would be happy again for a week or two. But, after sitting for 5 years I couldn't coax the carbon off the valves that way, hence the teardown at about 126k miles to clean them. After that resto I learned about adding oils to the gas we now have to prevent this sort of thing, and it fares far better.
