Oil furnace 'stutters'

I get my 25 yr old oil & hot air furnace serviced every other year.
Last fall there was a new kid at the place where I've had this done for 20 yrs & I watched him tune it up. He actually seemed to be doing a more thorough job than his more experienced predecessors. He was the first one in years to open the plenum & vacuum the top of the heat tubes.
But he didn't do the ?CO2? test-- where a probe is placed in the stack. I asked him about it & he passed it off with a 'we don't do that any more'. The old guy that was 'watching' him didn't disagree.
He left & for a couple weeks the furnace seemed fine--- but then it started this random 'stuttering'. [or I started noticing it] Maybe once every 10th [or 20th] cycle you can hear the furnace start-- then stop-- then start - sometimes as many as 5-6 times. The next cycle is always perfect. I've spent hours sitting beside this thing to try to figure out exactly what is happening, but I've never caught it actually acting up. The blower fan works steady through this stuttering so I've ruled out an open in the electrical feed. If I remember correctly the photocell will trip the reset button after the second try. So far it hasn't tripped the reset button at all. [ I 'tested' the reset button this fall when I changed the filter & forgot to bleed the line-- that tripped it.]
Another random and discomforting problem is some exhaust smell on rare occasions. I think I did catch this one once-- The burner fired & though it sounded good, there was a lot of smoke & it was coming out of an old probe hole in the stack-- and around the damper in the chimney.
This fall I finally decided to pull the nozzle & look at the ignitors. I was sure I'd found the problem as the ignitors were set to fire exactly even with the nozzle head. [.75, 80degree hollow cone] I re-set them to 1/8" ahead of the face of the nozzle, 1/8 apart & 1/4 above the hole. That seemed to do the trick-- but I've heard it 'stuttering' a couple times since.
I don't get any of the pre or post combustion 'pops' that would indicate unburned fuel being left in the plenum. I do smell burned fuel outside sometimes if the wind is just right. I don't know if this is just when the furnace is doing its 'stuttering' thing- but it is also random. I've never seen any smoke coming from the chimney.
This is a one line system & the *new* tank is outside and about 5 feet higher than the furnace. Filters were replaced this fall & there was no sign of gunk or water in either one. [I have 2 inline filters because I had an old tank under the eaves & I added a filter in the low spot of the line to catch water.]
Any thoughts on what might be causing the intermittent 'stuttering' of the burner?
Jim
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snipped-for-privacy@email.com says...

CO - Carbon Monoxide. Tests for a cracked or otherwise defective plenum. Not a bad idea to have a CO detector in the living space (unless your house is rather leaky) anyway.

Speculating here, but could it be the thermostat that's not making a reliable contact?

Partial flue blockage? Or maybe just an occasional down- draft due to wind conditions.
--
Mark

The truth as I perceive it to be.
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Then its not set up right at all. Period.

It could be a couple of big issues. Wrong nozzle setting, wrong air setting, cracked heat exchanger.

Unless you had the specs on the burner, and the little tool that sets them, they could be still wrong...as information.

You dont have to have smoke in the case of a wrong amount of combustion air.....as in too lean.

See above...also, pump sucking air, pump strainer clogged, shaft stripped, etc... From the description of what your tech did, honestly, find someone that knows what in hell he is doing...knowing part of the way to do it, isnt the right way to do it.

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The furnance in my home is even older and sometimes stutters. The best this thing to do is to have it serviced. Chances are when the oil company delivered oil, the muck on the bottom of the tank got into the lines. I bet you will have your oil filter replaced and the ignitor cleaned and everything will be OK. Gook Luck.
John

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