So -a long story. Currently it will light but every time is a challenge of yellow flames, soot and frightened cats. I have fitted a complete service kit including needle and jet/nipple. There are no leaks. A .177 BB will go in one side of the preston loop and out the other. The jet is marked primus and is rated @350. When it does light it seems to be a bit gurgly. But no sign of fuel warming up or being pushed back through the NRV. Once it is going it also flickers more than I would expect it to. Paraffin when decanted through a filter is clean. The burner gap is 15.5mm so maybe a little more than it should be and the paddle is vertical. The mantle is from Juliands generic but seems OK and is rated at 350. The "J" tube (mixer) does glow cherry red. I am giving it 40 pumps and two cupfulls of spirit to heat. Once it is running the mantle settles down and there is no aura. But sometimes there is a green tinge to the flame as it settles down. I have reviewed the restoration of a petromax website (very useful) and followed advice given there. So if anyone has any ideas/experience to share I will be very grateful. Otherwise this is going on the shelf. Chris
You sometimes find that rolling some fine brass mesh around the cleaning needle below the preston loop can help with flickering and it should help with the heat transfer as well. I would not expect the J tube to actually glow. If that is the case it is usually because of back burn, but that is something you can't mistake from the noise it makes. The biggest drawback with these lamps is the position of the preheat cup. Being pressed into the plate means it is too low to do it's job properly. A couple of preheats usually works, but you say you are doing that.
Well, if the mixer U or J-tube glows cherry red, its definitely not working properly. That'll cause the flame at the burner end/mantle side to be yellow. The fuel-air mix is burning inside the J-tube and turning it red hot. A 'back-burn'. If it could eventually settle down normally, then don't bother. This burning in the tube problem can be caused by a number possible reasons. Among them:- 1. Pressure too low and the flame in the mantle propagates back into the tube. 2. Partially broken ceramic burner,/meshing or the holes being too enlarged, causing the same effect as the above. 3. The J-tube is worn or defective(might not be visibly noticeable). Nothing much you can do to repair this. Replacement usually cures the problem. Sometimes deflecting the mantle's rising hot gases away from the J-tube surface might help. 4. The temperature within the J-tube gets above the autoignition temperature of the fuel-air mix for some reasons.(poor venting, worn jet leading to overfuelling and overheating by flames outside the mantle.
I have an Optimus 200 from the 1930's, and I have done just about everything and I still can't get the flickering to stop! Last resort will be the wire mesh up inside the vaporizer. If that doesn't work, to the shelf it goes!
Thanks everyone - I can confirm now that the loop is totally clear. This "back burn" (and it does make a nasty gurgling/roaring noise), I think it the root of the issues. Pressure is good (pump almost immovable) The jet is new so I must suspect either the ceramic or the J tube. The ceramic is cheapest/easiest to get so I will order one. I have also ordered some brass mesh too. to be continued... Chris
Out of all possibilities, I've had the most common cause being a defective J-tube. On mine, the tube did not appear to be appreciably worn or badly deformed or anything that would grab anyone's attention. Pretty strange but I believe there could be some metallugical changes(probably loss of zinc from the brass) in them or possibly pitted on their inner surface. This might affect the flow dynamics of the fuel-air mix, with eddy currents possibly induced. Effectively, that could cause the mixture to 'dwell' for a longer period than desired in the tube instead of flowing smoothly to the burner. That in turn greatly increases the chance of the mixture's temperature itself rising above its autoignition point, because it could no longer effectively remove heat from the J-tube to prevent it from overheating by the ambient hot gases. Eventually, the hot fuel-air mix ignites inside the tube and then sustained by the fresh incoming mixture. The mantle would quickly dim off on such an occurence, sometimes accompanied by a yellow flame and sooting.
Yes - this has the ring of logic about it. The breakdown of the material may also explain the green tinge seen in the flame. It does have a pitted surface too. Chris
Whatever the possible explanation for the phenomenon, the solution is pretty straight forward. Just try another vaporizer and see if that's really the cause.
Hmm, from the info, i would deduce the J-tube and related components like the clay burner and chamber might be the actual cause. But most often its the J-tube. You might want to try this approach as suggested above. new Petromax mixing tube with heat sink? heat spreader? Green tinge flame is a sign something is not burning right. My vapalux will do this more often than the Pmax styles, often telling me the vaporizer or burner has too much carb or they hate the kero mix.
UPDATE. As luck would have it a second Optimus 350/350CP came my way. This worked well after adjusting the jet/j-tube distance. I transplanted the inner top to the original and it still misbehaved. Although the back burn had gone it still flickered and lighting was difficult. So two problems ? well I will share (for the benefit of others although it is a little embarrassing ) that I had not managed to get the cock spindle in the correct part of the excentre (operating rod). This stopped the bottom valve from sealing properly, and resulted in the very sooty and orange start-ups. Furthermore I had not done the nipple/jet up tightly enough which was also allowing carbon to build up inside the vapouriser and probably also affecting the burn. It now lights up easily up with a single pre-heat, burns brightly and quietly and is flicker-free. Good as new ! The old J tube has dents in it and is mis-shaped around the thread, no doubt resulting in a poorly performing gas chamber. A new one is on it's way. Hopefully I will shortly be a two Optimus household. Thanks everyone for the ideas and inspiration. Chris
