"smoke" coming from under oil furncer burner

I have a 21 year old Carrier oil furnace that yesterday started making an unusual smell, hard to describe, maybe sort of acrid.
Tonight, at the start of the weekend of course, I found a modest amount of "smoke" curling up from both the left and right sides of the burner. On the left it's right between the round air intake and the wall with the fire chamber on the other side. On the right, no air intake but same place.
I haven't used a mirror to get a better idea of the source. It's sort of hot when the furnace is running.
I thought until Monday I could just plug the hole with GE Hi-temp silicone sealant. I've seen that used on my neighbor's identical furnace and it doesn't seem damaged by the heat. But I haven't found the hole.
Of course tonight is Friday, and it's cold out, so I'd like some advice to get through the weekend warm but without making things worse. Or maybe until the middle of march, when I'm going away for two weeks and I shouldn't need heat when I get back.
The CO detector is brand new, upstairs in my bedroom and shows zero CO, although I really have no way of knowing if the detector was bad when I bought it. I guess they test each one at the factory?
Any help would be appreciated.
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Probably sooted up and not drafting properly. Time for a clean and check by a pro. Here's hoping your HX isn't cracked.
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