A quick re-cap of my problems:
• This is a few days after a brief overheat (thermostat problem, fixed)
• Puts out a 232 more often than occasional, once or twice a 214
• Once or twice hard to start
• Popping sound at the rear end, about once every second

Things checked so far:
• Brand new FPR a few month old
• Vacuum hoses (bellows) all tight, new air filter
• New fuel filter

O2 sensor test data from today (procedure according to Lucid’s post (written by Bruce Young?):
• With O2 sensor connected to ECU ---- 0.1, 0.78 constantly cycling
• Open loop (O2 sensor output disconnected ---- 0.03
• Fake Full Lean ---- 0.9
• Fake Full Rich ---- 0.019 (with 1.5V battery)
• 0.017 (with human connection to 12V)

This looks to me it’s a good O2 sensor. However, is the O2 sensor known to have intermittent problems?

I also took this opportunity to test my spare O2 sensor using the propane torch method (never dare to do this before!). While the probe is glowing hot, it reads 0.9 with the torch on and 0.15 off. This surprised me. I thought it should be just opposite. When torch is on the probe, less O2, lower reading.

I assume that the popping sounds indicate a rich condition as it's cycling. Does it mean it's too rich? Any idea why?