They dont seem to be draining right, and they are brand new.
I am pretty sure that your problem isn't so much the cartridge but the preparation of a new atomzier.
Getting a new atomizer wet enough to perform right is usually the source of that burning nasty azz (LOL) flavor! New users usually scorch a new atomizer pretty good before they learn the importance of plenty of liquid
inside the atomizer, rather than being concerned about filling the cartridge.
Once a new atomizer is scorched the bad flavor usually hangs around. You may need to clean the atomizers you've vaped while too dry. If so, some PGA and soaking for a few hours usually does the trick to remove that scorched flavor. The PGA (such as EverClear or a good quality Vodka will do) will evaporate, so no need to rinse with water. Just blow out the PGA well and be sure to reprime the atomizer well with the same method for a new atomizer (below).
Best method to start off with a new atomizer is to blow out any primer (optional, I don't find any bad flavor with the primers being used today) put a good 3-4 drops of your liquid on the internal metal bridge in the atomizer, and let it sit for a few minutes to soak in well and distribute into the metal fiber inside.
Fill your cartridge, moving aside the filler to release air pockets and fill to the point of a glassy wet top.
Gently draw to start
vaping the new atty and add more liquid one drop at a time to the bridge at the slightest off taste or if you aren't getting vapor. You may flood it (gurgling) but it should be able to
vape through it. You can blow it out a little bit if you find it annoying or if you flood to the point of no vapor. Keeping a wet bridge helps the liquid to flow more smoothly from the cartridge to the nickle foam surrounding the atomizer pot. The bridge and nickle foam is what transports the liquid to the area near the atomizer wire (Important!!). I've gotten into the habit of adding a drop on the atty bridge for all models
each time I top off a cartridge.
Also, since the 901 and 510 atomizer cartridge are so small, they use liquid quickly so you will need to refill quicker than you expect, especially since you were used to the cartomizers. If you get in the habit of adding a drop of liquid to your atomizer bridge each time you refill your cartridge and you shouldn't have any more problems with burned hits.
Cartridge filler is the bane of vaping existence! Sometimes the cartridges (especially with polyfill) will refuse to let the liquid flow after a while. You can use a toothpick or paper clip to move the filler about to release the trapped air which is preventing it from flowing and refluff the top of the filler. I keep one with my liquid to poke at the filler each time. The straw modification can help polyfill release liquid better (see below) and allow trapped air to escape. Also, make sure you keep cartridge fillers at the top of the cartridge, as it can slump down. It needs to make contact with the bridge in order to transport down into the cartridge (and if you are wondering... no, it won't burn!).
Here is the link to the other cart fillers mod options you can try:
http://www.e-cigarette-forum.com/forum/ask-veterans/93586-best-cart-mods-510-atty.html
