hot metal small + CO

I have a 23 year old Carrier nat gas furnace, model 58GP125. Last spring and now in the early fall I noticed a strong 'hot metal' smell coming from the furnace when it is on. After a few heat cycles the CO detector in the house goes off. So I think that the flue is blocked and it's not venting properly, but it couldn't be any cleaner. Nothing but some light rust dust in the vent pipes. The furnace otherwise runs fine. No weird noises, burners have a nice blue flame, fan runs fine, new air filter. Good air flow at the registers.
I'm stumped. I haven't taken the furnace apart to fully inspect the heat exchanger.
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On Thu, 07 Oct 2010 15:23:16 +0000, blackhole531_at_gmail_dot snipped-for-privacy@foo.com (alfred) wrote:

    You have a death wish, I take it ?
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Suggest that you do.
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Forever is a really long time.... Especially towards the end.



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On 10/7/2010 10:23 AM, alfred wrote:

Years ago, there was a product sold at the supply house that when sprayed into the return air of the furnace would cause the burner flames to change color if there was a leak. I haven't seen it at or noticed it at the supply house lately. I could check when I go by today and see if it's still available. Here's a link to some information that may help you find a possible heat exchanger leak.
http://preview.tinyurl.com/2dte46d
TDD
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ain't no "stumped" to it, you have a problem with a jurrasic furnace that is most probably terminal(cracked or compromised heat exchanger). Your furnace past the upper end of usable service life. They don't last forever. Bite the bullet and have a new one installed. A new 2 stage, variable speed furnace will most probably pay for itself in just a couple of years in energy savings alone. Yes furnaces are more expensive now than what they were 23 years ago, but then so is everything else.
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