Optimus 930 Carburation

I came across another 930 the other day, and after a quick clean up, it lit and blackened a new mantle just like my others. I do know these are finicky little chaps, and there has been much discussion about mantle blight for these and others. I decided I had to get the bottom of the problem, and whilst doing so I have stumbled on something that helps and may be of use to others experiencing similar frustrations. I've needlessly expended more time and mantles on these over the years, than any other lamp model, and played around with all sorts of fuels including neat white gas.

The problem had to be a mixture one, and the J-tubes were getting cherry red so combustion was evidently taking place too high up and behind the nozzle. With the hood off, and using a thin tube to blow through, I steadily directed air up inside the orifice of the tube so as not to impede the flow of vapour, I found to my delight that the sooted mantles on all my patients cleared in just a couple of seconds. Replacing the hood brought eventually back the blight, so I concluded air flow was being impeded. I then prised up the top inner plate about 4mm above its normal position, and hey presto, blight gone and running in their normal bedazzling manner. Only downside is the holes for the bail handle are thus obscured, and you can't fit it without pushing the inner cover back down.

I'm coming to the conclusion that the J-tube orifice needs to be a little higher, and the carburation design of these (and maybe others) was a borderline pass/fail in the manufacturing process. I suppose as jets age they can enlarge, but all mine are marked 200, so I'd not imagine a lot would be wrong.

I'd be grateful of the observations of more learned members on this please, before I conduct my next experiment, which would be to saw off about 5mm from the downspout of the J-tube, so I can push the cover down and fit the handle, and have improved the air mixture to something more like accurate.

 

What has me wondering is that the majority of these experiences are from people living in the UK. Is it a fuel issue? I have very rarely had any problems with the 930 and have used quite a few.

 

Hello and thank you for the input. I've wondered at length myself and tried a variety of fuels, including neat panel wipe, as well as mixtures of the two and all with the same sort of dismal results. I'm thinking the issue seems to be more with air mixture than fuel. Whether UK imports were in some way different I know not.

Anyway, as an initial test, I've stuck a copper washer between the J-tube and the internal mounting, and the bottom of the downspout is protruding only about 3mm now. So far running fine, and on white spirit too. Another problem I can see is getting a good seal under the jet, as you can't tell if additional fuel is escaping into the tube there when lit other, than by the smell of it. I've filed out copper washers to size to sit the jet down on.

 

Just as an update, here are a couple of pictures of my currently lit one and where the downspout is set now, and the other is obviously a lot closer to the jet still. There was a bit of a discrepancy between them it must be said, of about 5mm to begin with. I achieved the "raise" on the lit one, using one thick copper washer, but may have to saw some off the other when I'm more confident I'm on the right track.

 

@ROGER BAKER

I wouldn't be running that lantern on pure naphtha (panel wipe). It doesn't have appropriate safety features for gasoline.

Tony

 

Thank you Tony. Just used PW briefly as a part of the process of my "scientific" study into tuning these. Actually, I've a couple of Veritas Superb lamps, and you should try getting one of those to run right on anything remotely like paraffin ! They have no so called safety features either I suspect, but they do rather like white gas! Cheers, Roger.

 

Roger

The Veritas Superb is anything but superb, going on the various comments from people here at CPL.


Cheers

Tony

 

Ah yes, unless you switch to a gasoline fuel. Mine run very well indeed on PW. I agree, they are not very Superb as many are inclined to say, that is, if you are following strict guidelines when it comes to fuel. I'm often wondering if Kerosene had more bang for your buck when these were marketed.

 

Sawing off seems a rather radical and permanent modification, as replacement J-tubes for the 930 are not readily available.
It could be a good idea to start off with the standard 300 cp jet and needle and proceed from there with various mantles etc.
An important step would be to ensure that the Preston loop on the upper vapouriser is clear and not partially blocked.
I have a few 930's and have fettled quite a number and have never experienced these problems.
They tend to be boringly predictable and reliable when in good fettle.

 

Thank you for your observations. I've three of these, all with presumably their original jets, and all are 200's. I've tested all the loops and none were obstructed. The intrusion by the downspout into the mixing area was slightly different on each patient. So far I've "jacked" them up with washers, and all are now running happy as Larry. You can only go so far up before the top bend hits the roof of the hood however. I am pondering whether these J-tubes "wilt" and bend downwards under heat, thus altering the mixing rate. After all they are not supported, and do get very hot indeed. I wouldn't like to try and bend one back up if that's what is going on, so cutting a sliver off seems like more of a temptation. As said though, all are behaving well now I've opened up the gaps. I'm happy with the diagnosis, and the "fix" (but still wish the red control knobs didn't melt, seemingly if you give them a serious amount of use !)

 

Obstruction is one thing, and easily checked.
But how did you do to really clean out the loop thouroughly?
I often see that people who are having problems with "Preston looped lamps" actually never really de-coked the loop for real. It's not always a heat and quench is enough, but more mechanical means are needed.

 

The Optimus 930 is a 300cp lantern and uses a 300cp jet. Using a 200cp jet would theoretically mean a 33% leaner mixture which may cause problems including overheating. Motor car engines that run too lean tend to melt holes through their pistons. If the knobs are melting you definitely have severe overheating and the way to fix it is to first go back to stock standard spec. before experimenting further.

 

No matter how thin the washer under the jet is, it's raising the jet and decreasing the air gap. A light smear of copper based grease on the threads will ensure a good seal without reducing the air gap.

Henry.

 

Thank you once again Henry, I do take your point. And thank you all. As I've been banging on about the carburation all along, I still hold that the blight is in my cases at least, caused by running too rich, and by introducing more air, the carbon soon burns off and I'm left with a big smile as they all now run spot on. I'm thinking of re-visiting some of my other troublesome loopies with this in mind. (Radius 119 in particular)
I've only one 930 with a badly charred knob, and it came like that, but on a lamp in its original box that didn't look to have been used more than a couple of times. I've noticed a good many others out there on the web with rather sorry looking ones too. Maybe a duff batch.... I thought it was generally accepted that these do run quite hot, and so it's probably a good job the tanks don't hold more fuel and run hot a lot longer on a fill.

 

A slightly loose jet will cause the burn to be too rich with blackened mantles. You can sometimes check that by pressurizing the fount with fuel, lowering the pricker and closing the jet orifice hard with your finger. If there are some bubbles and fuel at the jet/generator interface, its clearly leaking( which you might not notice when the lantern's in operation).
Worn or enlarged-orifice jets are some of the most common causes of overly rich mixes.
Sometimes the lower generator/fuel pick up part has not been screwed sufficiently down into the fount, resulting in the jet being at a higher position, or effectively a reduced air gap between the jet and J-tube inlet. Also check that the Preston loop generator is original and not a replacement unit that's longer/taller than the original.

 

Great advice, thank you. I had wondered what best practice for testing the seal round the thread of the jet would be, and you have provided the answer, though I suspect you could end up in a bit of a mess trying to do it by yourself without an assistant.
Many thanks, Roger.

 

It's not a UK issue, believe me. I have a very nice 930 but it sets on the shelf because if you don't constantly keep an eye on it, when lit, it goes nuts and the J tube glows cherry red. I burned out the first one when I got the lantern, and I had no luck with the second J tube replacement. It's a shame.

 

Hello George, and I think you should take consolation in not being alone with these. I've one in its original box, that looks for all the world like it was lit just the once, overcooked itself, and got put away. If you go up the dialogue you may be able to see some of the journey/learning curve I've been through to at least get the things to burn off the soot, and run bright. That said, and pretty as they are, I'm not sure they are entirely my cup-of-tea as I like to keep the chill off in the house of an evening with a lantern, and these do give off a bit of a more noticeable Kero odour. Try raising the downspout with washers, and see what results you get. I'm all ears, as I only posted this, not to be carried through the streets as a valiant hero, but thinking others too, may at least stop wasting money on mantles, methylated spirits and above all else time, hope and enthusiasm !

 

A red glowing J-mixer tube is rather different from a rich/lean fuel-air mixing issue.
For this, you get a severe 'back-burning', in which the major part of the flame is being sustained somewhere inside the tube instead of outside the ceramic burner cap.
I've had a number of such occurences on similarly-designed lanterns.
There had been a number of earlier posts by other members here and elsewhere on the discussions regarding this. There are various reasons or causes being found, stated or hypothesized. Partially blocked jets, reduced fuel-air flows, mixing tube/chamber overheated, cracked burner, worn or enlarged outlet holes on the burner cap to name a few.
I never really found a conclusive reasoning on mine but had that rectified just by replacing the J-mixing tube with all other parts and parameters remaining the same as before.

 

I'm thinking these are just too finicky, and yes, you are correct in there having been much already written. I had this problem with what looked like an almost new lamp, and think there are some mighty fine looking examples, lit once and put back in their boxes, perhaps in disgust after a disappointing first outcome. I reckon they were just too fussy about how they were set, and even minor variations in build from new, threw up a certain proportion of duds if the word can be excused.

I'm happy to have "tuned" the three I have by simply moving the J-orifice up as far as I can. It seems to eliminate combustion above the nozzle in any case. Certainly, gently blowing a little air up there through a small tube does rapidly burn off the soot, which otherwise can only get worse. You can then see more clearly what the adjustments you've made might have altered. Saves having to tie another mantle on and hope for the best too.

 

If memory serves me, Radius made a lantern like the Optimus 930, but, I think slightly larger. It looks like a "clone" of the 930. Anyway, I wonder if since the Radius and the 930 looked so much alike, if the Radius lantern also experienced the same problem?

 

I'm intrigued by what I seem to have found after considerable expenditure on time and frustration, as I have a number of lanterns, mainly Preston loop models, and including a Radius 119, which have been put to one side having blighted their mantles. I think I need to re-visit some of these with a different approach to air mixture anomalies, rather than fuel quality & jetting problems. I've had Tilley burners obstructed by spiders nests before now, that look like they've been stuffed with wadding, and seemingly unaffected by heat !

 

These are basically Petromax-like.
As for me, I'd test them, including the clones, with pure 'highway' diesel from a pump station. That'll be about the heaviest fuel you could burn in those lanterns. This will coke up the Preston loop sooner but it'll still burn flawlessly white in the mantles with no sooting when the lantern's properly tuned.
If it could burn diesel, any other lighter fuels (kerosene, white/mineral spirits, etc) would be a piece of cake.
Do not attempt using petrol, white gas or light napththa as most of these lanterns are not designed with the additional safety features required to operate with volatile fuels.

 

@ROGER BAKER

Reading through your list of woes; noting the views of others who have commented that they do not have similar issues with the same lamp(s); and noting your comments regarding the Preston Loop, I ask whether you are sure you have open, clear Preston loops?

The reason I ask this, is that blocked and partially blocked Preston loops are, in my experience, the most common source of black mantle disease in Australian-made Aladdin 1As (which are virtually copies of Radius 119s).

Preston loops can be a real bugger to clean thoroughly. Heat and quench works to some extent, but I always resort to stainless steel wire, carefully bent at the tip, and threaded through the loop while being twisted, until it emerges from the lower hole.

I then test how clear the loop is by rolling a small ball bearing through it. This all takes patience.

I’ve had remarkable recovery of Preston loop lamps after clearing the loop.

Cheers

Tony

Edit: Crossed with @MYN

 

Hello Tony and thank you for the update. I started on this "journey", thinking there was a simple tweak that would make a difference. I did note how some others also, had inexplicably experienced blackening after seemingly faultless running. The air-gap between the jet and the J-tube orifice varied quite a bit on all my studies, and simply by raising the tubes, albeit clumsily with washers, it seems to have made enough difference to get all three up and working nicely. Quite why there was such a difference I'm not sure, but perhaps the J-tubes can "droop" and close the gap.

If my observations, and personal outcomes can enable anyone else to effect a satisfactory recovery, and at no expense, then I will be glad to have at last made a positive contribution within the fraternity. I fully respect the fact that we all have our own take on things, and in our own ways, have pondered the anomalies between seemingly identical lamps.

I've only rudimentarily checked the loops for "flow" by blocking the restriction inside with a bit of soggy tissue paper and blowing through them. I can imagine that a good thick coating of Carbon inside the wall, would reduce the preheating of the fuel, but those I've poked at with piano wire seemed to have yielded very little in the way of soot-fall. I've successfully barbecued and crunched out a heck of a lot of soot from vaporisers, and some that you can't even get the wire out of at first.

I'm pretty confident a proportion of these 930's can be just plain temperamental, and the design and perhaps small stature can see them go "out of tune" because of something very minor, and that in my case, has seemed to be a "marginal" mixture issue.

As an aside, whilst you can run Tilley Vapalux etc perfectly normally without glass, I've been unable to get one of these running without a globe. I've three of these, and I'm a globe short at present, and have had great fun in all this, swopping the globes around without breaking one! I think they need the heat contained within the glass to function, such is their absolute requirement for everything to be "just so".
Cheers, Roger

 

While it is always interesting to read of peoples experiences and experiments with lamps, for any serious investigation it is useful though perhaps pedantic to bear the following in mind:

A founding principle of the scientific method of investigation is to control for variables. For any findings to be generally applicable and repeatable it means starting with a known base line and observing the results of changing only one variable at a time.

In the present case that would be a 930 in good factory trim complete with its 300cp jet.
Starting with a different jet or one in unknown condition will necessarily invalidate all the results from being of general application.
These variables would include jet, vapouriser, air gap, needle adjustment, fuel and mantle.

 

I have several 930, all but one, always worked very good, in fact i think the 930 is one of the best lanterns i know about, all my 930's came with 250cp jets.
The one that gave me trouble had a small hole in the mixing tube where the set screw is, put in a new tube and the lantern works fine !

When the lantern was running with the defect tube, the tube started glowing red and the lantern would eventually dim, and burn outside the mantle (flames)

Fred.

 

Even though the 930 is labelled as a 300cp lantern, all the burner parts have the same dimensions as the Optimus 200. Therefore a 200/250cp jet works best. A 300 jet will work, but the setup has to be just right.

 

I have always thought that Optimus were pushing the limits a bit on the 930 and even more so on the rare 350cp 930 variant. More so on the amount of heat than on reliable working though.

 

Well, all mine including the one in its box that looks to have been lit once, has all the kit it was sent out with from the factory, mantles, can, tools, and including a new spare 200 jet and needle. I think it likely as all mine came over time and from different sources entirely, that I'd say they were sent out with those jets. They are all rather annoyingly bright as well, as I don't have a reflector, and easily achieve a brightness to rival any of the best performing lamps I have.