Primus 991

Discussion in 'Fettling Forum' started by Darryl Durdin, Feb 19, 2020.

  1. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi fellas, can i get some advice on what may be wrong with my lantern,
    20200219_141547.jpg
    I have the orange flare around the mantle,
    When i stipped cleaned and put back together, i replaced the small pricker and the jet bought from the bay, for primus 991, it all fires up ok but it dosent get any better than this.
    Ive used big and small mantles.
    The air tubes are not blocked or obstructed.
    The original jet and pricker were flogged
    Its seems to be a fuel air mixture thing but im open to suggestions.
    Thanks
     
  2. AussiePete

    AussiePete Australia Subscriber

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    Hi Darryl

    I’m not familiar with this breed of lantern but it looks to be running too rich. That is to much fuel for the air mixture.
    First thing I would suggest is to put a thread sealant paste or similar around the jet before screwing it in. I have had a lantern recently, with a new jet, that was getting too much fuel, burning just like yours. The extra fuel was escaping the generator from around the jet’s thread. Sealing the thread solved my problem.
    Second, as I said I’m not familiar with this breed, however does it have a screw in the “J” tube just above the where the jet shoots it’s fuel. If it does this screw operates a butterfly inside the J tube, like a carburettor on a car. You can adjust the butterfly’s position to alter the fuel/air ratio mix using a screw driver and twiddling the screw.

    I’ve also heard that the height of the J tube’s opening from the jet is fairly critical. It can be adjusted by loosening the J tube clamp, lower or raising the J tube and retightening the clamp. Maybe others can help here.
    Hope this helps.
    Cheers
    Pete
     
    Last edited: Feb 19, 2020
  3. Matti Kucer

    Matti Kucer Sweden Subscriber

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    IMG_2738.JPG
    Hi!

    It looks like this, so no adjustments as far as I can recall.
     
  4. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Just like above, no adjustment, i will check out the jet, when i tested everything i had no leaks but i can asume when its hot and expanded the gas can come out easiest route.
     
  5. AussiePete

    AussiePete Australia Subscriber

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    Hi @Matti Kucer
    And @Darryl Durdin
    You are right, as I said that I don’t know this breed. I was thinking that a Chinese clone, an Anchor 999, would be similar.
    I guess I need to get one of these Primus lanterns now. What a good excuse. :lol:
    Cheers
    Pete
     
  6. Tive

    Tive Sweden Subscriber

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    These are noisy little ones, if you got the right pressure and correct fuel feed, sometimes the wire mesh inside the bottom of the fuel feed tube is clogged causing low flow of fuel.

    If so, the wire mesh can be punched out with the right size drill of proper lenght, from the top and into the fount. I had to do this once, on a lantern behaving like this.

    The J-tube is screwed on the air feed tube and can be adjusted by screwing it up or down ( rotating it ) around the air feed tube.

    The alcohol fuled variant of this lantern, the 391, uses a restrictor in the bottom of the air feed tube, if you have one of these restrictors inside there, you must remove that one in order to run it on kero.
     
  7. Nils Stephenson

    Nils Stephenson Founder Member

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    That certainly looks like it is running too rich. Where did you get the new jet from? I'm wondering if it was a jet for the 981 instead. The part number for the 991 jet is 6348 whereas the part number for the 981 jet is 6438. Easy to mix up as the thread is the same.
     
  8. Matti Kucer

    Matti Kucer Sweden Subscriber

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    And the needle is part 6347.

    Screenshot_20200219_150554.jpg
     
  9. MYN

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    If the parts are right and the problem persists, you might want to check if the jet is shooting out a sharp, vertical stream of fuel. If its shooting sideways or at an angle or spraying/dribbling a little, you'll get an inadequate fuel-air mix. Usually due to some dirt blocking the orifice.
    Or if the J-mixer/air intake unit is a little bent or not in-line with the vaporizer/generator, it brings about the same effect as the above-mentioned.
    If you really need to adjust the air-gap for an 'unadjustable' design, you could try fitting in a piece of suitably-sized washer at the end of the vaporizer around the jet as a spacer before re-assembling the J-mixer cum air intake unit.(this could only increase the air gap a little, which might or might not be helpful to get a leaner fuel-air mix).
     
  10. JEFF JOHNSON

    JEFF JOHNSON United Kingdom Subscriber

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    That's sound advice in the previous posts and here is my tuppence worth, I have had new jets slacken with the heat and simply tightening them with a spanner has cured the problem.
     
  11. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi there, this is what i bought of the Bay, said
    Jet and needle for primus 991/992.
    It has no more detail than the packet.
    Ive followed the tips from above and i have a slight improvement, it started out a bit rich but did settle as it got hotter, no orange flare but the mantle did not brighten up it was dull white.
    It seems to lack the pressure hiss , its there but not distinct.
    It has a good stream of fuel , i even pulled it apart when hot just to see the vapur and that looked all good.
    There dose not seem to be any obstruction in the fuel pick up in the tank.
    The air tube can be unscrewed raising the J tube buy a few millimetres but that did not improve matters,
    I will keep trying, thats the fun thing about lanterns 20200220_093103.jpg
     
  12. Nils Stephenson

    Nils Stephenson Founder Member

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    The jet and needles must be new production. They look well made but it is hard to know what size the hole is. From memory it should be 0.17 mm. Definitely not bigger. Screwing on the mixing tube will not change anything. The height is fixed by the construction of the top of the air tube. The screw adjustment is only to make sure that the air tube and mixing tube sit flush where they press in. In my experience with this type of burner, it is either the jet or the air supply. Are there any serious dents in the air tube or mixing tube? How snugly do they press into the burner?
     
  13. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi there Nils, it all fits very snug there is no slack in any of it, there are no dents in air tube or j tube, generator, font is good, i have digital callipers i will measure the wire, i have micro drills ill carefully see what fits, the old jet has a distinct bigger jet opening, i was thinking it was flogged out, i may try and replace the old jet just to see if it is different.
    Process of elimination
     
  14. Carlsson

    Carlsson Sweden Admin/Founder Member

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    There's always the posibility that the vapouriser is coked up.
    Are you sure that you have brushed it through enough?
    These straight vapo's without a preston loop are extremely easy to get clean, but they are also picky about wanting to be pretty clean inside in order to work properly.
    But as Nils said; you can't be absolutely sure that these semi-proffessional after market jets are correct. Best would be to get an original Primus jet.

    But try to see if it helps to restrict the jet a bit by slightly raising the needle when you have the lantern running and hot.
    If slightly raising the needle improves the light, you might suspect that the jet is too large.
     
  15. MYN

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    Is that kerosene you're burning? I don't see a positive shut off valve there but you could try mixing-in a little gasoline or better, Coleman Fuel/naphtha and see if it improves anything.
    The straight vaporizer is not as efficient as the Preston loop type if you're dealing with kerosene.
    At times, the dimmer burn could also result from less than ideal vaporization. If some brass gauze or coil could be fitted into the vaporizer, it might improve heat conduction from the vaporizer to the fuel.
     
  16. MarkC

    MarkC Subscriber

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    I suspect the nozzle as well. Have a few of these, and they are so simple. A straight tube generator, and a fixed airgap.
    Mine all ran very well, and I installed all NOS jets. Still have the old spares if you are interested.
     
  17. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi fellas, i will endevor to follow your tips and sugestions, its a cool little lantern, im keen to see it in it full glory, its all about the fettle, to fix or make as new. Ill be dreaming about it or staying awake thinking about it, all week end.
    Great hobby
     
  18. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi fellas, i followed your tips and advice, it now dose not orange flare, i thoroughly cleaned the fuel uptak, generator needle rod, i cleaned it with firearm solvents , snake cleaner, wire brush, and a bit of hydrochloric acid,
    Ive used a long mantle to see if this helps vaporization,
    I may have to check out my leather cup pump, i seem to be doing alot of pumping, the NRV is working, im thinking maybe not enough pressure.
    I will investigate. 20200221_183120.jpg
    Joy, joy to be had
     
  19. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    Hi fellas, itz been a journey but i think i have it.
    I revered the leather cup, put it back in and now what a difference with the pressure. 20200221_184759.jpg
    Thanks fellas for all your tips and advice.
     
  20. AussiePete

    AussiePete Australia Subscriber

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    Well done Darryl. Persistence wins the day. Good to see it running.
    Cheers
    Pete
     
  21. Darryl Durdin

    Darryl Durdin Australia Subscriber

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    And now the money shot,
    Im very impressed with this little beauty.
    Very bright 20200222_014754.jpg 20200222_014859.jpg
     
  22. george

    george United States Subscriber

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    Ah yes, Primus! I'm glad to see you got it straighten out. These are a fine lantern and you have a nice one! I have four Primus lanterns: two1020's (1935 and 1955), 1321 (1941) and a 1001 (1930). Out of the three, my 1001, grand old lady, runs the best! The two 1020's were hell to run! I can't recall how many times I had them apart! They suffered, or at least looked the same as your Primus when you were having trouble lighting it. I finally got them to work by reducing the pressure. Mine take about 18-20 pumps. They run fine but if I put in more pressure they start to act up after 10-15 minutes! Nature of the beast, I guess. Starts burning outside the mantle with a slightly orange flame. The 1321 I haven't even lit. I have not had it apart so I can't tell if it's still set up for alcohol or it was converted over to kerosene at sometime. It has a hard to find globe made in France not Germany!
     
  23. MYN

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    Thumbs up
     

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