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Thread: Weil Mclain oil furnace smoking after DIY tune-up

  1. #1
    DIY Junior Member
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    Default Weil Mclain oil furnace smoking after DIY tune-up

    Hi All,
    First timer on this forum, been a lurker for quite some time now. Wife and I moved into our first home about a year ago and with this economy we've been trying to minimize our costs. One of the things I tried to avoid is having to pay for yearly furnace maintenance by doing tuneups and repairs myself with the help of my dad who also has an oil furnace in his home. We did a tune-up today on my Weil Mclain furnace. We replaced the oil filter, replaced a bad shutoff valve right before the oil filter, cleaned out all the soot, replaced both electrodes and replaced the nozzle. Furnace turned on and fired up at first try, however smoke came out of the (draft regulator, I believe this is the proper term) and continues to come out every time the boiler first fires up(but stops smoking after about 10 seconds), but will smoke again at next fire up after being off. After some digging and reading I noticed that the nozzle that we installed is a different specification. The one we replaced says "80a 85" and the one we installed today says "85 60". We left the air intake settings the same but I think the problem of the smoking is because of the different nozzle. Therefore requiring proper calibration with a combustion analyzer? I learned quite a bit today while watching my dad. I'm a car fanatic and realized that this sort of works similar to a cars engine.....fuel, spark, air gives you what you need, and I see this problem as us changing the engines fuel injectors to a much larger size without also increasing the air intake volume (although in a car the ECU normally compensates with more air) in the furnace this air compensation is a manual thing and therefore the air to oil mixture is now OFF, or too rich. We played around a bit with the air intake setting to try and balance it out, and we were able to minimize the smoke but it's still smoking enough to bother. Our next step is to put the old nozzle(which seems to still be ok) back in tomorrow and set the air intake settings back to exactly how they were(we took a picture). hoping this will place the furnace back to the calibration it had before we started tinkering.

    Am I correct in my findings?

    should I be concerned for the health safety of my family with this like this? We've got several smoke and co2 detectors in the house and none have gone off, but we can definitely smell the odor throughout the house a bit and my eyes have been burning a bit since it started smoking. I've left our patio and deck doors opened for a few hours now to get some fresh air inside.

    I don't feel safe with this situation so I've shutoff the furnace until this is resolved. Luckily tonight and the following 2 nights will not be as cold out so we can manage with our space heaters in the meantime.

    I've decided to stop being cheap on the important things and I will go ahead on monday morning and set ourselves up with a service plan with our local oil delivery company. some things aren't worth trying to save a couple of dollars on, not when it comes to safety. I'll let the professionals with the proper equipment do this going forward.

    Any suggestions or confirmations is greatly appreciated.

    Thanks in advance

    --Rad

  2. #2
    In the trades Dana's Avatar
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    Unless the jet was clogged or something, why did you replace it? Do you have the old one? If it works, put it back!

    Yes, the fuel/air mixture has to be adjusted correctly to get full combustion without leaning it out to the point that it's too low for optimum efficiency (or in the extreme, making an explosive mixture to make things a bit too exciting on igntion.) In addion to the fuel rate rating, the jets also differ in spray shape.

    If you're replacing the jet, always replace it with something of the EXACT same ratings unless you're intentially raising or lowering the BTU rating of the unit (a whole other subject.) Even then adjusting the air for optimum combustion efficiency is something that should be done, particularly if you're seeing soot buildup (an indication of a too-rich mixture, cold-operation/short-cycling, or both.) If you're not going back to the old jet, you can eyeball the flame while adjusting the air and get it to where the flame-tips don't look dirty, but that's still not a substitute for adjusting it with a combustion analyser later, or putting in the exact manufacturers recommended part for the burner type & rating the furnace is set up for.

  3. #3
    In the Trades Tom Sawyer's Avatar
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    It is impossible to touch most anything on an oil burner without having an analyzer hooked up to check the adjustment. The nozzle change alone is probably not what is causing the smoking problem but... a lot of the new equipment is quite sensitive. Having a professional come in is the right thing to do, not only for peace of mind but also because an improperly adjusted oil burner can cost you more money to operate.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    As Dana noted, changing the jet, changes the mixture. It is also possible that the new jet is big enough, even if it was adjusted properly, your output could be significantly more than needed, and the heat exchanger might not be able to handle it. Bad mistake. Fix sooner, rather than later! You'll never get the best, maximum efficiency burn without the proper combustion analysis tools. Over the course of the winter, this can be quite expensive and it may be pay now, or pay later when your fuel use goes up. Never priced a combustion analyzer, which might be an option, but then, you need the knowledge of how to use it, too. Also never looked to see if I could rent one, which might be an option, too.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
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    We put the old jet (thought it was called a nozzle) back in place and placed the air settings exactly how they were. Essentially, all that is different now is new oil filter, new gasket, new electrodes(same settings) and soot has been cleaned. It sounds and looks(flame) as before.

    I'm going to start calling my local oil distributors tomorrow and get pricing on having someone with a combustion analyzer come and adjust my furnace for maximum efficiency. At least for now the smoking has subsided and I feel calmer. A quick google shows combustion analyzer in the $600+ range, not only is this quite pricey, but I would also have to learn how to use it properly! I'll let the pro's handle it.

    We replaced the jet because we have no idea when it was last replaced, we had a new one on-hand (not realizing that it was a different rating until afterwards), so we figured let's replace it with this new one; and for no other reason.

    Thanks all for the advice and suggestions.

  6. #6
    DIY Senior Member zl700's Avatar
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    "80a 85" and the one we installed today says "85 60".

    You cant arbitrarily just install any oil nozzle. The correct one must be installed as per manufacturer. Putting in the .85 was up sizing the oil rate and BTU's. Also the original was a "A" meaning hollow fire pattern, what was the new one hollow, solid, semi-solid, ......

    Also the 85 means angle and you put in a 60 degree which means a tighter pattern, possibly not fully igniting and causing unburned oil build up in chamber, not too mention a over fired, incorrect pattern could destroy the target wall in the combustion chamber quickly.

    Yes there is potentially some danger, probable product damage and so on.

    Stop fooling around, get a tech that has the equipment and knowledge to set the burner up correctly before its destroyed or a visit is paid by the fire department.
    If Payback is so important to you, why are you not driving a Toyota Corolla?

  7. #7
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    Quote Originally Posted by zl700 View Post
    "80a 85" and the one we installed today says "85 60".

    You cant arbitrarily just install any oil nozzle. The correct one must be installed as per manufacturer. Putting in the .85 was up sizing the oil rate and BTU's. Also the original was a "A" meaning hollow fire pattern, what was the new one hollow, solid, semi-solid, ......

    Also the 85 means angle and you put in a 60 degree which means a tighter pattern, possibly not fully igniting and causing unburned oil build up in chamber, not too mention a over fired, incorrect pattern could destroy the target wall in the combustion chamber quickly.

    Yes there is potentially some danger, probable product damage and so on.

    Stop fooling around, get a tech that has the equipment and knowledge to set the burner up correctly before its destroyed or a visit is paid by the fire department.
    We put it basically back the way it was(except for oil filter and new electrodes), including the jet that it had.
    I'm taking your advice as well as everyone else's very seriously.

    Thank You.

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