A few weeks ago I would have said - you haven't loaded it completely, or something along those lines. In the recent past, I've had well filled cartos greet me with a burned taste from the get-go, so I'm assuming now that this is just an accident of some sort that can just happen. In most cases, if a carto tastes burned once, it will always taste a little burned from there on, so I just toss them right away.
For what is worth, here's what I do to fill a cartomizer:
- I always wear a condom! If you don't put the bottom condom on, juice will pour out
- I make sure the needle is between the filler and the outer wall, not into the filler, and push it as far as it goes
- I inject in three different places on the circumference
- Once liquid comes out of the center hole or from the sides I let it soak, then draw back on the plunger; then I push again, let the whole thing get fully flooded, wait, then draw back on the plunger. I do this several times. I wait more for thicker juices.
- With the condom on, I suck on the mouth end. What that does is pulls all the juice from the center hole into the filler. It's counter-intuitive, but you do not get juice in your mouth
Once it's filled and I made sure it works okay, I punch it and stick it in the tank. I never put an empty carto in a tank.
I use a 1/4'' self tapping saddle valve to do the punching, and I am completely sure that the pre-punched ones have too small a hole anyway, so I quit buying those early on.
Once in the tank, especially with thick juices, I found that it helps to "prime" it from time to time by taking short, sharp draws on it without pushing the button. You will see bubbles coming out of the holes indicating this works.
Interestingly, I also found that once a tank goes halfway, it may help to pull it up, that is pull it over the top of the carto and putting it back on. What this does, I think, it removes a partial vacuum that may form inside the tank, although I can't really bring myself to believe such vacuum should form in the first place - it just works.