Alcohol stove issues

My guess is that the air temperature might be lower and your burners takes longer to bloom.
Don't know what fuel you are using but 95 to 97% of it should be alcohol, the rest is water and or additives.
In other words if your alcohol had evaporated you would have almost nothing left.

Yeah. I'm using 70%. Just weird it worked fine rather first time. I'm going to get some new stuff tomorrow and test it out.

I make similar stoves and do very well with 97% and poor to barely okay with 70% when I test them out. 70% mix helps me determine which are the better made ones and which ones are not great. It seems to be around the minimum that my good ones will make a decent looking flame. I would not use 70% in the field.

I'm hoping a scientific person will tell us why your stove worked with it one time but not the next time.

Ah, you are using Everclear or something like that.
Well in that case yes you are using 30% water…
I was thinking about SLX or Yellow Deet but yes I do know that some are concerned about those fuels (I am not…)

It's really hard to tell based on limited information.

Fuel type is important, as others have mentioned. Blocking wind is important. The ambient temperature is important.

If you place the alcohol reservoir onto a cold surface, heat is lost there, so the alcohol can't warm up to normal operating temperature like it needs to. Get some hard flat insulator and place the stove on it before lighting. See if that works better. For the field, you could use anything like a small piece of Masonite. To insulate mine, I have three or four layers of aluminum foil crimped together.

–B.G.–

Not all Alchy stoves are created equal. I've seen some very tempermental designs that would be frustrating on the trail. I like Minibulldesign because he tests each in real-world use – not on a stove top.

"To insulate mine, I have three or four layers of aluminum foil crimped together."

A small piece of cardboard would be more insulative, methinks. And lighter?

Different water temp, air temp, barometric pressure, windscreen orientation, humidity? The unreliability of isopropyl? Or just simply that alcohol stove efficiency changes after an initial burn in, especially in something that has a liner and/or paint to burn off.

Not really enough info to go on. If you're choosing isopropyl intentionally, then so be it. If you're just checking out pop can stoves for the first time, then switch to something like Yellow HEET or Denatured alcohol (Marine Stove Fuel).

I glued some felt on the bottom of one of my stoves for insulation.
I don't remember which one but that particular stove suffered from conductive heat loss (I would think that it was a pressurised type…)