Is this burnt plastic flavor you describe a dry burn? Could it be once you get that into your mouth that is all you can taste? It's nasty and not only sticks around in my mouth but takes a couple of good puffs to get it out of my 4072s.
I haven't bothered to completely figure it out on my 4072s because they're old and junk but it seems to revolve around when the batteries blink from being on too long or the cartridge is running down. It can happen even when the cartridge is full.
To translate that to a manual battery, you're holding the button too long causing it to burn faster than it feeds. With 2 atty systems doing the same thing and your battery reading correctly I'd guess it's something in your technique.
I agree a dripping atty would be your fix. Although that's not a good out and about answer.
I just had both my 4072s doing that, I dripped a little and it was fixed.
I haven't bothered to completely figure it out on my 4072s because they're old and junk but it seems to revolve around when the batteries blink from being on too long or the cartridge is running down. It can happen even when the cartridge is full.
To translate that to a manual battery, you're holding the button too long causing it to burn faster than it feeds. With 2 atty systems doing the same thing and your battery reading correctly I'd guess it's something in your technique.
I agree a dripping atty would be your fix. Although that's not a good out and about answer.
I just had both my 4072s doing that, I dripped a little and it was fixed.