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 ;-)