My hypothesis is that a proportion of fuel arriving at the burner is pre-vaporised, having evaporated as it flows through the hot pipe to the burner. What's supposed to happen is that alcohol arrives at the burner in liquid form. In pre-gasified form, there's simply less fuel there.

I agree about the vaporising inside the hot pipe. However, if the burner was being preheated sufficiently, there is only gas coming out of the feeding nozzle. It is actually a quite interesting design, as the gasified fuel is mixed with air after it exits the feeding nozzle before it is lead through the actual burner and then burns just like a gas stove... I will try to take some good fotos.

One more thought: Is there room for pressing a heat shield between the stove and the tank?

Unfortunately not... Or I don't see it. 

I tried my idea leaving the nipple cap on, and also tried to add some slight pressure from my lungs, as you mentioned, Arne. No difference observable, neither way.

If I remember correctly, that stove transports the fuel to the burner via a wick.

That would be quite interesting, indeed, Toni! It would explain a bit, why slightly pressurising the tank didn't show a significant effect. However, it would not explain that when the valve is opened in cold state to fill the preheating dish, there is some fluid flowing out rather fast. Too fast for a wick, I would guess. Did you open it up once?

Regarding the HPV Salsa, would it be a possibility to fit a remote tank to help keep the fuel cooler and well away from the heat from the burner?

Sure, but it would mean some replumbing and soldering of that bronze fuel line... A rather invasive surgery. Before taking such a measure, I would like to understand what is really happening when its burning longer then some minutes.

does the grease nipple have its spring loaded ball valve still within its body?

I of course removed the tiny ball and spring before installing the nipple ;-)

Not wishing to hijack this thread, but as it's about stoves and cookers, I wonder if anyone could suggest a readily available material to use in a trangia to soak up the alcohol, in a similar manner to the Origo does.

Maybe it wouldn't work in the Trangia, but it would help prevent spills if it did.

Regarding the HPV Salsa, would it be a possibility to fit a remote tank to help keep the fuel cooler and well away from the heat from the burner?

Asmat wrote:

As for Arne's idea of pressurising the fuel tank: fingers in ears, everybody.

Ah, chicken ☺ !

Now, there is pressure and there is pressure. I didn’t mean to add pressure anywhere near that in a Primus burner. That would have been analogue with installing that ethanol tank in the mast top.

I was more thinking of adding pressure enough to emulate rising the tank with 10-20cm. To do that, one only needs to blow with a pressure of about 8-16hPa (milliBar).
One could simply press a petrol hose over that grease nipple and blow quite gently in it while watching the flame of the burner.

One more thought: Is there room for pressing a heat shield between the stove and the tank?

Arne

But now you got me thinking: if I would just leave the grease nipple cap on while cooking, that might impose at least a little pressure from the heat expansion of the gases inside the tank... As precaution strategy I can fill the stainless ikea dish with 1 cm of water, so that the Salsa thingy is sitting in water.

Maybe I try this. Maybe.

Hm,

So why should the power drop because of the hotter ethanol?
The only change I can imagine is that the liquid alcohol expands and become lighter per litre. This may reduce gravity force to feed the burner.

What if you tried putting the tank under some pressure?  As a quick test, I suggest you light the burner and wait until the power drops. Then you bring out your bicycle pump (..which I bet you have on bord...) and then try to gently add some pressure on the tank via that grease nipple. If the burner flares up under added pressure, you will have a method:
A one- or two-litre bottle is fitted with a bicycle valve and a hose to that grease nipple on the stove’s tank. The pressure in that bottle will only need to be topped up now and then. At a pinch, before you get that bicycle valve in place, you can simply raise the pressure by pinching the bottle.

The added pressure may even supercharge the burner a little to speed up cooking or roasting...

Just an armchair idea...

Arne