Some doubts about this Primus.

The complication can be expected more or less, since its a hybrid of various Primus models.
I've cleaned the Preston loop with extensive heating and quenches, alkali immersion, water flushes and solvent rinses. Finally blowing oxygen gas through the dull red-heated loop to burn out any remaining carbon. But I'm still only 90%(at best) confident its sufficiently clean.
On the pulsing, I'm baffled. There isn't any obvious loose connections but I'm not sure if the 'Leidenfrost effect' or any flash vaporization could have taken place inside the generator as it gets hotter.

One thing I'm pretty much quite certain though:
The phenomenon always only occur when all the parts have been really heated up(with hood attached), after 20-30 minutes of good burning. Its definitely a good deal hotter than during the spirit preheat.

 

It is a pity your lamp did not come with the 1080 hood and inner hood. It does seem to be an overheating problem. The 1051 hood and burner cage may not provide as much air flow as the 1080 hood would have. Could you try to insulate the J-tube to keep it cooler? Maybe more asbestos string...
Do you have a good gas seal where the J-tube enters the burner?
Does the jet sit at the optimal height inside the mixing chamber? Perhaps try shimming it up a millimeter or three.
I also think, seeing that the 1080 and 1020 are both 300cp lamps, your lamp should be able to draw sufficient air without the extra hole.

 

@phaedrus42
Well I've no choice but make do with whatever I've got now.
I have plenty of asbestos string/rope/strips lying around and no problems buying them as they are still widely used here. Sure I could insulate the tube.
I was having the same thoughts as you about the the sealing where the J-tube enters the flame spreader. I'll see if I could improve on that.

Just before you mentioned this, I've found that the top surface of the jet might not be sitting at the height that I normally feel comfortable with. From my measurements with a vernier caliper, it seemed to be too far beyond the center axis where the air tube intersects the chamber. I'll try shimming it up 3-4mm and see what happens with the extra air tube hole remaining closed.

Anyway, I've removed the tube to check for any tiny leaks and cleaned it up a little:

 

The nickel still looks very good. You can try sunscrewing the 2 tubes a bit from each other if needed. Sometimes they are screwed in a bit too deep.

 

Thanks @phaedrus42
I'll give almost everything a try to optimize the performance which whatever's available to me.

 

How are the two tubes attached? Originally the 1020 mixing tube screws into the chamber at the top of the air tube (see my photo), but there is no thread on this part of the 1080 mixing tube. Has someone cut a thread on this or are they just pressed together? Maybe the 1080 part is pushed too far into the chamber giving too small an air gap. I wouldn't think so from the way the mantle burns, but I've run out of ideas.

 

@Nils Stephenson
I'm not sure if its threaded or pressed into the chamber as I did not separate the two.
It does nor seem likely that its threaded on that part as it could be impossible to screw in as the air tube would be in obstruction as the J-tube is turned.
It does not seem likely to be lacking in combustion air toi from my earlier tests.

 

Here's another later update:
I've wrapped the air/mixing tube with asbestos string and coated it with copper antiseize slip, just for a test. Looks a little disgusting:


I've also added a nickel-plated copper braiding into the generator. Here's a picture of the braided sleeve on the pricker rod:

Re-assembled the lantern with a liitle adjustment on the air gap with the mixing J-tube mounted 3-4mm higher than before. Here's the lantern burning-in with spirit to remove oils from the antiseize:

After that, I put the hood on and lit the lantern as before. The previous combustion within J-tube was gone. The pulsing/flickering stopped and the fount was much cooler than before. Here's a picture of the lantern operating well beyond an hour without the previous problems:


But its having a new problem. There was a slight(near invisible) flame halo outside the mantle.
Worn jet or not enough air this time? The kerosene's fresh, clear, clean and colourless.

 

I don't really like the asbestos wrap. My feelings that the mantle is burning a little less brightly than before.
I'll remove the modifications one by one, including the blocking of the additional air hole and see if the previous problem returns.

 

The halo would seem to indicate a worn jet.

Good luck with the fault finding.

 

Thanks @Nils Stephenson
I'll try to improve it somehow, other than replacing the jet(since I don't have any spares yet). At least its still shooting the fuel straight, not skewed or spraying all over.

 

I fitted a new rosette type Auerlicht mantle to my Primus 1001. It formed very nicely, but was a bit dim and had a bad halo around the mantle and even above the burner. at higher pressure. The lantern has a brand new jet and had no halo with the previous mantle. Wasted the mantle, fitted a DT-140 and the halo is gone. There are definitely differences in performance between mantles. I've experienced the same phenomenon with Petromax 500cp mantles that I got from the USA. Changed to an old Coleman silk-lite and it cured the problem.

 

Thanks for the info @phaedrus42 .
I've broken the earlier mantle while dis-assembling it again on the 2nd trial.
The 2nd mantle did not form as nicely as the first. The earlier one burned brighter without a visible halo.
Maybe, this could be a factor too.
I removed the asbestos insulation on the J-tube mixer and the earlier problem returned. But this could also be due to excessive heating on the tube by the external flame(quite significant) halo during the 2nd trial. Not too sure yet.

I've adjusted the J-tube higher for the best light output from this unit.

 

Hi all,
After trying almost everything without any Primus spare parts at hand (almost giving up too), I've finally been able to completely sort out all the previous faults.
Now its running without the combustion inside the J-tube, no overheating and without the extra asbestos string insulation wrap.
No more pulsing and no more flame halo outside the mantle.
I have adjusted the air gap between the jet and mixing chamber(J-tube) to the maximum and replaced the clay burner nozzle with a slightly larger ceramic(Petromax or Butterfly 350cp size) burner cap with a metal screen/mesh inside it.
Lit and tested it for more than an hour with the hood on. Deliberately operated it at a slightly higher than normal pressure (between 2.5 to 3 bar).
Appeared to run satisfactorily. Thanks for all your inputs, which kept me thinking, exploring and questioning myself on my own understanding on such devices.
Here's a snapshot of the lamp after all that:

Note the extra brass flame spreader above the original unit. That's for connecting the much-raised J-tube to the original flame spreader.

 

Well done

Btw, how did you adjust the height of the mixing tube and do you know what height it ended at?

 

@Nils Stephenson
I estimate that the jet's tip is now very near the bottom level of the air tube intersection.
With the aid of an extra Petromax type flame spreader piece to join the J-tube to the original Primus flame spreader.

 

BTW, I found this in one of the earlier threads here too:

 

Well done Myn and now you can enjoy your lamp!

 

Thanks @phaedrus42 for sharing some lantern experiences, which I've never knew about before.

 

After a rich experience of technical research you get the reward of light

Congratulations

Regards,
Titoo

 

Yes, that is the original drawing for the jet. The thread no. 21 is the one I mentioned earlier at 7mm diameter and 35tpi Whitworth.

 

@Titoo , @Nils Stephenson ,
I've just searched the parts catalog for Primus 991/1020 and Primus 980/1080.
I think the main reason why I had some rather serious troubles during lighting up and running was because the generator and burner cap assembly belonged to a maybe a 980 or 1080 but the air and mixing J-tube belonged to a 991 or 1020.
And perhaps the jet was also somewhat worn(which I had to make do without replacement).
I think the air-to-fuel ratio was a little too low, which meant it was running rich.
With the modification done by a previous owner, I can't use gasoline (as for 1050) so that it could run leaner.
Therefore, I had to add some 'adapting' pieces so that it could run with a good light output and without the flame being started or drawn into the J-tube.
Also, I included two layers copper braiding into the generator to stop pulsing.

@Nils Stephenson,
I don't think I can find any dies or taps for gäng no.21. I can find Whitworth fine thread toolings but they're in inches and I couldn't find 9/32" with such fine as 35tpi pitch. Its customized partially to metric 7mm as well?

 

Congratulations Myn .
I have enjoyed this post very much.

 

Thank you @ROBBO55

 

Unless you can make the thread yourself on a lathe, it is easier to buy new jets. As mentioned they are available, just not on your side of the world.

I'm glad to hear that the result is satisfactory. Just goes to show that someones ingenuity in the past was not a waste of time.

 

Thanks Nils.
I don't think I would be able to easily purchase any spare parts from Fogas.
Indeed, despite some serious and unusual modifications, the lantern is actually performing better than I've expected
Pumped it up to higher pressures, and its output matches that of a Petromax 500cp.