Hi guys newby here asking for help please ,I have just got hold of a primus 71 stove and needs a bit of a service, can you tell me which seal goes in here as it is leaking , please see picture also is it correct it runs on petrol , and I can't undo the nut that holds the burner riser to the tank ,seems to be very jamed up ,any help would be appreciated,
Welcome! There is plenty of info on this site, if you know what terms to search with. These stoves were designed to run on petrol when new, since then petrol has changed composition and is no longer suitable. You need to find pure naptha- in the UK this can be purchased in the form of Aspen 4T (intended for garden machinery), solvent based panel wipe, Holts brake and clutch cleaner in 5L tins, or Coleman fuel which is stupidly expensive at £9 a litre. The cheapest way to fuel the stove in the UK is to buy two of these, this means free postage and ideal fuel at £3 a litre. Edit to add- the term 'white gas' will get you blank looks in the UK, it's a term which has never been used here. The seal for the control spindle isn't a spare part as such, instead a strip of graphite is purchased, wound round the spindle and 'squished' into a solid block on tightening.
You can still use unleaded petrol in a pinch - just don't stand downwind. Nasty half-burned chemicals from all the additives they put in these days - it'll give you a massive headache. But if you really need to do this, use the cheapest gas you can - they put less additives in it to keep the price down.
In the UK the cheapest petrol has the highest ethanol content, 10%, even further from the fuel these stoves were designed for.
Huh... In the US, they put ethanol in the fuel mainly during the winter months. Has something to do with forming smog in the winter inversion layers. Would it's use in a stove simply decrease the energy content? Can't think that it would harm the stove at all.
All UK petrol contains ethanol for environmental reasons. Being derived from vegetable matter, it is claimed to be good for the planet (ignoring the impacts of producing and transporting the stuff). Cheap 95 octane fuel contains 10%, the premium 97 and 99 octane fuel contains 5%. In this thread Staffan Rönn mentions that one of the reasons Optimus state not to use automotive fuel in self-pressurising stoves is due to non-linear expansion which can be almost explosive in pressure buildup. I have no idea which component in modern petrol casues that effect, whether it is additives or ethanol. Ethanol has been added to petrol for decades now in some parts of the world. Either way, pure naptha is safer and cleaner burning and can be purchased fairly cheaply for the amount these stoves use.
To me the terms 'petrolburner', or petrol stove, distinguish such liquid-fueled stoves from 'keroburners', or kerosene stove. The terms don't imply that pump gasoline is the preferred fuel. Naptha, 'white gas', Coleman fuel are all petrol as far as our stoves are concerned.
Thank you @Blackdog I have not heard it that way. Makes sense with the octane. I see 10% ethanol all year long. Winter only?
I stand corrected. They reduce the ethanol content in regions of cold weather, not increase it as I stated. Makes it easier for the cars to start in freezing weather.
Digging in to this "non-linear expansion" thing. Apparently Coleman fuel boils at 208F (98C), whereas ethanol boils some 36F (20C) lower. So I guess the problem is that if the fuel tank gets hot enough, the ethanol starts to vaporize faster and eventually boil, which causes the pressure to spike, and the relief valve can't vent it fast enough. More pressure means more heat output from the stove, and you get into a runaway situation. What do you all think?
I agree, I use the term 'petrol stove' to describe these, but the term does rather imply pump fuel so I always take care to spell things out clearly to newcomers, in context for whichever country they reside. It was put forward as a possible cause of the trouble in this thread. Not proved for certain, but it's enough for me to avoid using it and advising others against it, given that very pure burning, very safe fuels are readily available. That's my reckoning too, but I'd love to have it confirmed. The lower boiling point of ethanol is certainly a pain. I gave up last year and replaced the mechanical cooling fan in my car with big twin electric fans. Regardless of ignition timing it overheats in traffic on 95 and 97 Octane, and I can't afford the 99 Octane it can cope with! So cheap fuel and brute force cooling. Whether it works due to keeping the cylinder head temperature down, or keeping the general underbonnet temperature down to stop the ethanol boiling in the fuel lines is widely debated, but it works! Sorry for topic drift....
