The more I think about this as I keep this thread in the back of my head, I must agree with Barneymg. Actually, I had the same thing happen to me with my Sprite!
I too had a stuck valve. Initially it was only while on the highway. When this happened, I took my foot off the gas then hit it hard, and the valve freed-up. Eventually, it stuck solid and I had to re-do the guides.
On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"