Hi here are some photos of a well-used Primus No.71 dating from 1939, which I received a few days ago. The burner of this particular model is fitted with a rotating inner shield which allows some throttling of the air supply to the burner: I renewed the filler cap washer (the original was leather held in place with a central brass screw). I also added a new flame-plate and control key. The stove operates well and easily passed the coffee test! Best Regards, Kerophile.
Nice one Kerophile, another rescued. Your stove is burning really well. I have not seen one with the rotating inner shield. Are you able to remove your flame plate for pic?
Hi Ron, I found that the restrictor didn't make a lot of difference at sea-level, where I live. The photos were taken with the restrictor fully open. In the closed position the air inlets of the burner basket are around one-third closed but for me the flame-pattern still looked good. I will examine the effect in greater detail next time I fire the stove up for a "brew". I will also try to get some detailed photos of the restrictor operation as requested by Rick. Endy has already shown some great pictures of the restrictor operation on his beautiful Primus 71: https://classiccampstoves.com/threads/15622 Best Regards, Kerophile.
Good sound stove and tin, George. Too often I've had ok Primus 71/Optimus 80 stoves but with tins having the pot rests rusted away. Those of an age to have the rounded filler cap and the solder pin excess pressure safety release are a favourite of mine. John
If ever there was a definition of 'been there, done that', that stove would have to be it! Wish it could talk.
what fascinates me most in many of these picnic stoves is not so much the stove, but the traveling case/stand... i would love to see modern renditions of these for the 123R (as it is the only brassie left in commercial production AFAIK)
George, Very nice early model 71. I did a perusal of the catalogues and it looked as though the 1937 parts catalogue has the flat filler cap but I can't tell for sure since it is a drawing. So could this be one of the earliest, if not the first, of this model with the rounded filler cap, burner bell control, and the tin style together? The burner control in the bell doesn't show up in any of the catalogues until 1954. It probably would show up in a 1940s parts catalogue but there isn't one to look through, AFAIK. It's piqued my curiosity a bit as to which year was the first for this style 71L, since I have a ' 53 that's similar. sam
Hi Rick requested some photos of the rotating throttle/mixture control mechanism, fitted to the burner bell of this stove: The first two photos show the mixture control in the open position: The following to photos show the shield in the "closed" position, where approx one-third of the area of each aperture is covered: Finally you can see the small lever by which the shield is rotated between the open and "closed" positions. The lever follows a curved path between the two rest positions: The control is intended as a air/fuel mixture adjustment between "pure" gasoline (petrol) and gasoline blends. Running the stove on un-leaded petrol this afternoon. I had a nice blue flame pattern with the apertures fully open. Once the shield was activated there were yellow tips to the flames, indicative of a fuel-rich mixture. Best Regards. Kerophile.
Hi George, am curious since it restrict some of the air, would that work also for alcohol? Was thinking if the 111T has a restrictor for alcohol, would that kind of setup also work or would it need also a jet to get it to work as intended.
Hi Ron, In principal a burner with a means of altering the fuel/air mixture can accept a range of fuels. However, alcohol has a pretty low calorific value and I suspect it will be outwith the operating envelope of this particular Primus No.71 burner. Perhaps the use of a larger aperture jet would allow it to work with alcohol if the stove will self-pressurise. Please don't ask me to try the experiment. I am not a fan of the use of alcohol in pressure-stoves. Best Regards, Kerophile.
Hi George Just doing my Primus 71 homework. Have you tried a Berniedawg cap on this burner ? If so does it function with the air throttle adjustment feature ?
Hi Andrew, I have not yet tried a BD mini-burner on this particular stove....So many stoves, so little time! There is a snow blizzard blowing through here at the moment, but I will give it a go when the weather improves. Best Regards, George.
Thanks George I am PIG Sick of snow !!! last year was bad and now it has come all too early this year !!! And me from Dorset !!! last time i saw a fair bit of snow at home was feb 1978 !!!!!
Hello Kerophile, thanks for the detailed pictures of your 71. I appreciate it. Take care and stay warm!
Hi, Gary's mini-cap works great in an Op.80, so I am confident that it will perform faultlessly in a Primus 71: https://classiccampstoves.com/threads/11908 It will be interesting to see what, if any, influence the damper has. Best Regards, Kerophile.
This was the basis of my question, as to the operation of the mini cap coupled with the damper. And while on the subject of 80's and 71's ..... Looking at the tins, All of my 71's have the two rows of five holes at the base of the case. Then during the change to A B BACHO the vent holes were changed to ten verticle slots running around the tin in a more central position. Comparing the Primus tin to the Optimus tin, this has only two sets of three horizontal slots at the base. My question is WHY ? Was there a performance issue, and if so did it make a difference ? OR is it merely cosmetics
The inbuilt restrictor in George's stove doesn't restrict the air enough to operate the stove on alcohol. At least 2 of the large slots would need to be completely blanked off. I had an 8R running on alcohol a few years ago with that much restriction and the standard petrol nipple. It was just an exercise to see if it would do it; I wouldn't be running any of these small petrol burners on alcohol as a regular fuel.
