Rumbling Oil burner puffs black smoke

Hello all, I have an oil boiler (ca. mid 80s, according to previous owner) that every now and then rumbles loudly (sounds like a truck going by outside the house), and spews gray/black smoke from what normally is the air inlet vent on the pipe that leads to the chimney. I have had a couple furnace guys over and they shrug their shoulders and say that unless it does it while they are there they don't know what it could be. I have had the boiler cleaned and the nozzles replaced. One of the guys said if he had to take a guess it might be sludge buildup in the oil tank, so I tried some sludge remover additive that I found at home depot. I figure that stuff is probably snake oil anyway, but it was pretty cheap so I figured I'd give it a go. Didn't really seem to do much. The repair guy stated that some sludge could be making its way to the nozzle that would then starve the combustion of the oil, this then causing the problem. So how do I make this stop?
The oil tank is in the basement and there is a copper line from the oil tank to the boiler. Would cleaning the line out help, or just replacing it? The tank looks old, and has some exterior rust, not a lot though. Could there be a lot of sludge buildup in the tank itself? The boiler works fine most of the time, but it does this every other day or so during the winter while it is running on a regular basis. I am in CT so it only runs right now for hot water. It happened to do it again a few days ago (hadn't done it for a long time), and it got me thinking about it and how to get it fixed. I'd like to try to get this problem fixed before the fall/winter hits us.
thank you,
Mark
--
"Travel is fatal to prejudice, bigotry and narrow-mindedness"
- Mark Twain
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Mark Holbrook wrote:

Does it also say "I think I can, I think I can, ..." ? :)
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<SNIP>
Sounds like late ignition to me. Burner comes on, sprays quite a bit of oil into the fire box and then lights. Could be a number of things:
Like Mr. Berlin says: Oil filter could be clogged.
pump strainer (if it has one) could be clogged (big culprit that a lot of techs overlook)
Pump may not be delivering the requires PSI (did they check it with a guage? Could show if the filter or the strainer is stopped up OR the pump is bad)
Transformer could be weak (sometime when they start to go bad they are sporadic)
Could be a hairline crack in one of the porcelains (this causes the spark to arc on the nozzle assembly instead of at the ends of the electrodes)
The electrodes could be set wrong (spark will arc ON the nozzle)
Wrong size nozzle
True, you can run into one that will not do it 99 times in a row and then on the hundreth time you got Choo Choo Charlie.
Unless you have a contraxt with the shoulder shruggers, you may want to try another company. Explain to them what it is doing and let them go from there....
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Wow, that is a lot of possibilites, I will make sure to print this out and ask each of these querstions of the person that I have come out to take a look at this. I very much appreciate your thorough response.
Thanks!
Mark
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Give us an update once they correct it....

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OK, took a long time for an update on this, but we ended up getting the problem fixed - since my posts in the end of August the problem seemed to just go away, then it reappeared a week or so ago in full force - turns out that the transformer was bad, as you suggested! We had it replaced and no more "Choo Choo Charlie" rumbling and puffing of smoke anymore, which is definitely a good thing.
So, now that that problem is fixed, I have noticed a new one upon inspecting the handywork of the repairman that was out to fix the original problem.
I noticed a slight sizzling/hissing noise, even when the boiler was off. The boiler also acts as a hot water heater with the use of a coil, which the previous owner had replaced when I bought the house in July of '04. There is a square metal plate on the upper right hand corner of the front of the boiler that has the inlet and outlet pipes for the cold and hot water into and out of the coil. There is a noticeable small drip of water coming from the left hand side of the gasket on that square down the front of the boiler. It has been going on long enough such that there is rust and the paint has peeled away from the area where the drip meanders its way down the front of the boiler. It then collects on a larger square plate where the oil pump interfaces with the boiler itself. It was around here where the sizzling was happening.
So now what should I do? I presume the drip is originating inside the metal panel where the coil is, and that tightening the bolts that hold that panel down really won't do anything, other than confine the drip to the insides of the boiler somehow - so I'll basically be covering up the problem by isolating it in that manner. If I still had an old coil in the boiler, I'd take a guess that it had failed and was leaking, but the fact that it had been replaced a little over a year ago makes me wonder if they only replaced the faceplate, and not the coil. Of course, that's unproven until it gets opened up, of course.
I'm a little annoyed that the technician that was out didn't notice this problem, but who knows. My assumption is that at least he didn't somehow cause the problem, as the rust seems to indicate that this has been going on for a while at least.
Any suggestions on what might be causing this and the best way to get it repaired?
Thank you so much for your earlier suggestions, they really helped out!
Mark

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