These are some great ideas. I think I have addressed some of them already. I checked with a propane torch to look for leaks around the carb and intake, and did not find any. It appears that the engine is/was running rich, as new plugs look like this after less than an hour of operation:
View attachment 1715909198
Six is on the bottom, and #1 on the top of the image. So the time on these plugs was before I replaced the carb. Doing a wet float check on the new carb, it seemed a bit high (2 or 3 32nds above the 27/32 level) so I adjusted the float a bit. And while I was at it, put the float spring in correctly; it was in at an angle. I would guess this is something that might happen in shipping.
I'll need some education on what "bopping" a valve entails. Is this tapping on the rocker arm over the valve with a hammer, or brass hammer, or plastic mallet; or with a wood block in combination with any of those? is it pulling off the rockers to hit the valve directly?
I don't think the fuel system is a problem; I tried running it with a 2-liter bottle of known good gas plumbed directly into the fuel filter and it seemed to run the same. I also dosed it with Heet to try and eliminate that as a cause; back in '86 that fixed a similar problem that came down to a load of bad gas I got while I was hauling a 2 axle U-Haul cross country. But that's a story for another time.
I'll get a 195 stat and try that also. What I heard "back in the day" was that to de-gunk an engine, you poured ATF into the intake till the engine stalled, then let it sit overnight. But your bopping method seems like a more reliable method of removing deposits.
Thanks for your thoughts and time.
Bill
