Hi All, I've an Optimus 350 that when I've tried to light just has flames around the mantle and the mantle goes black. I'm also having the same problems with an Optimus 930 too. Having read around the forum one problem maybe the gap between the burner and the jet. This is a bit of a dim question but how do I adjust it? I've measured the current gap at 17-18m and understand it should be 15mm. Looking at it there are two screws but I assume the adjustment screw is the lower of the screws nearest the jet? I thought I'd better ask how I do this before I make a mistake! Many thanks and apologies for the noddy question! Dave
No you adjust the gap by raising or lowering the J tube. These lamps do not really have adjuster screws except the screw facing forward in the J tube rotates a paddle inside the gas flow and normally that should be straight up and down. Optimus lamps are prone to this black mantle problem and they seem to be much less forgiving than most other makes. There may be several reasons for this but there are some things to check. Make sure the nipple or gas tip threads are not leaking as that can make the mixture too rich. You can seal that thread with either copper or nickel anti squeal grease. The generator may be running too cool so the right size and shape of mantle may be important. The generator probably needs a clean to remove any carbon build up. That includes cleaning out the preston loop. In the end it could just be that the hole in the nipple is enlarged though so if all else fails then maybe a new jet is the answer. ::Neil::
Lovely, thanks a lot for highlighting what I need to check. If I need to, how do I raise or lower the J Tube?
Depends on how it is fixed to the inner hood. Some lamps have a clamp but Optimus tend to fix the J tube with a pair of hex nuts just above the mantle cap. Mostly they don't need adjusting and won't move much anyway. One trick that sometimes works well is to lap the jet on an oil stone. Just enough to clean around the jet hole though. That can reshape the hole and enable a straighter jet of gas. Last resort though because once done and the lamp has been used you can't tell if it has been done before and there aint a lot of meat there. ::Neil::
On the 350 you loosen the lower screw you were mentioning which holds a clamp on the tube. It also has a point which usually leaves a dent in the tube. This sometimes makes it difficult to adjust the gap. As mentione the gap between the top of the jet and the bottom edge of the tube should be 15mm. I wouldn't expect 17-18mm to be the cause of the problem though. It sounds like you are getting too much fuel through which could either be a worn or loose jet or a blocked preston loop in the vapouriser. Sometimes a loose ceramic mantle holder can give the same symptoms. I am assuming you are preheating enough.
Hi, yes, preheating fine and the ceramic mantle holder was secure. I checked everything over and lit it again with the same result so I guess it is a worn jet.
I suspect the loop is blocked, see if you can set it up and blow air through the loop to test. Even if air does get through it's worth spending some time clearing it out. A good blowtorch can be handy as well as a bycicle gear cable for threading through the loop and chipping away at the carbon. You can use a magnet to see how far round you have got, normally the half way point is the most blocked. If it is badly blocked this process can take several days, but a small blockage can clear pretty quickly. Hope this helps James
Thanks, James. As it happens I bike a lot so must have some spare gear cable lying around somewhere that I can sacrifice!
