Why would my exhaust manifold be glowing red while ideling?

It's running super lean. Don't drive it like that

We can't figure out why it's running lean

Which motor are we dealing with?

Chevy 2.5

It's either vacuum leaks, low fuel pressure, fuel injector issue, o2 sensor or the pcm is going out

We have tested all of those and everything came up normal

What was the o2 reading? Or did you just replace it?

It was reading .05 so we replaced

.05 means it's reading super lean so it was probably correct. What's your fuel pressure at?

I have the same problem with a 1953 Bentley R type. 4.2 liter straight six with two side draft SU H6 carbs and a common plenum intake manifold. Car has not really run for ~22 years and I decided to get her going today. New points (has Delco Remey dual point distributor - stock for the R type) New plugs and also a condenser. Coil has internal resistor. I can make changes to fuel ratio by adjusting the jet position on the metering needle as done on SU carbs - And the engine is running smoothly and idling well and stable BUT as dusk rolled in I noticed the rear manifold was glowing red hot. I turned it off immediately Can one end of a manifold be lean? And yet engine run smoothly ? I do not believe there to be any air leaks on the rear carb/manifold Thank you realize this is very old school - I will take domes off carbs tomorrow and compare jet position on each just in case my adjustments made one very rich and other very lean - but my experience is that the engine is very finicky if not balanced Thank you First post