mexicanyella

I'd replace, or file and gap, the points, just to be sure. That's a dirty plug; either it's got a weak spark, or is burning oil, or is running rich. You seem to feel it was running okay for most of the ride, so I'm a little less inclined to say it's running rich, but was there any exhaust smoke? Black = rich, blue or blue/white = oil burning. My old hardtail Z50 engine is worn enough that it blows a little blue smoke after it's idled for a few minutes (probably worn valve guides allowing oil to come down the valve stems under high-vacuum conditions--idling--but it uses very little oil and the plug stays pretty clean and rarely fouls...unless it's time for a points setting operation.

So by doing the points and getting a known strong spark reestablished, you're eliminating a large variable.

It's worth it, while at NAPA or wherever buying your points file, to get a jet cleaner or torch tip cleaner, which is a little folding thing with a bunch of different stiff serrated wires hinged into it. Handy for cleaning deposits and crud out of jets. It doesn't take much crud to have an impact on fuel mixture. Sometimes soaking doesn't do it; it dissolves the varnish but sometimes particles of grit or dirt or fuel tank rust still remain lodged in there.

Also if blowing air through passages and jets with a compressor and nozzle, be aware that it's fairly easy to launch jets into low earth orbit.