Carlin Oil burner problem

I have a Carlin 99FRD with a Monarch 0.75 nozzle on a 1986 Burnham V-13A-T boiler for a FHW heating system in my own house. In the past year the burner has started burning rough (rumbles). The rough running starts with a heavy rumble on shut down and progresses to become rough throughout the burn over a couple of days. I've always had my oil company come out and check everything. They clean the unit, fire it up, and it runs clean (no soot dot), 83% eff, and smooth with a good flame- for about 2 weeks. Then it starts again with the burping shutdown. I'm pretty handy, so I've started cleaning the unit myself (can't be paying for a service call every two weeks). What is happening is the flame retention head is completely caked in carbon. There is a black oily residue on the nozzle with a discoloration on one side. I blow out the nozzle with compressed air, scrape and clean the head, and I go another 2 weeks. Any ideas what causes this behavior?
More info: The service guys say that if the burner were no good we wouldn't be able to get a good flame to start with. They have tried a few things and are baffled. I understand that Carlin had sent out a new tech bulletin on this model that suggested changing the air tube length. They did that. This one is now set at 2. There was a discussion that the oil line was clogged with residue or gum so a 10 micron filter was added at the burner end of the line. Then they thought the oil line was restricted by two filters so they removed the 40 micron filter from the basket on the tank end of the line. I took it upon myself to clean out the oil line with compressed air, filling and backwashing it 3 times. I've got a plastic milk jug 3/4 full of some pretty nasty looking black shit. But the last batch came out more pink than black so I think the line is pretty clean. There was a lot of little flakes and particles that stick to the side of the milk jug and don't wash off when you swirl the stuff around. Any help would be appreciated.
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Okay, now after everybody had a lot of fun, here comes the answer. BTW for whoever doesn't understand written word let me recap: - burner was fine for 18 or so years - burner works fine for a week or so after cleaning - gooey stuff came out of oil line during one of the cleaning sessions.
Here's the answer: sludge in the oil tank (bacteria growth) accumulated there during all these years because of water condensation in the tank. There's no chip fix though, tank has to be pumped out and flushed. Because of environmental shit it'll cost a pretty penny. To my customers I suggest to replace the tank and I take care of the old one for appropriate fee.
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On Wed, 22 Aug 2007 14:16:51 -0500, " snipped-for-privacy@pipeline.com"

No cheap fix but a very inexpensive precaution. Dont run the tank low. Low oil level promotes condensation in the tank. Use a tank that has a bottom tank fitting. This way you can install and elbow, short pipe and a shut-off. Then you can drain a little out of the tank once in a while to see whats in the bottom. Use a oil conditioner in the tank at each refill. And lastly, just get rid of the oil shit and get a gas unit or heat pump. Bubba
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"And lastly, just get rid of the oil shit and get a gas unit or heat pump."
couldnt agree with you more !!!!
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On Wed, 22 Aug 2007 19:10:08 -0500, "George McDaniel"

nice for the burner equipment but it doesnt so shit for the tank. Why not clean out the bottom of the tank once a month just like you're "not" supposed to do to a water heater? :-) Bubba

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