Here's ONE answer to your problem: Direct Dripping. Direct Dripping, or just "dripping", is when you drip juice directly onto the bridge of your atomizer, instead of relying on the cartridge filler to do that for you.
Notice the difference between the words "dripping", and "dipping". Dipping is a separate topic described briefly at the end of this post.
SEALED BATTERY:
First, make sure your PV has a "sealed battery". That means there is no hole in the end that the atomizer screws onto. Note that we're talking about the battery here, not the atomizer.
Liquid can leak into an unsealed battery through that hole, and ruin the battery. Now you know one of the reasons why manual batteries are so popular around here.
No hole? Great! Let's continue:
Take one of your cartridges and remove the filler. That's the stuff that looks like cotton. You won't be needing it anymore.
Now, open a bottle of your favourite juice, and drip a couple of drops onto the bridge of the atomizer. That's the thing inside that looks like an arch covered in very fine steel mesh (It's actually nickle foam). If it's dry, you will need to prime it with 3 or 4 drops. Afterwards, it will take 2 or 3 drops, depending on the atty. Start with 2, and adjust from there. It's easier to add another drop than it is to remove one, and I've found that atomizers usually need one less drop than I think they do.
Replace your empty cartridge, and vape (If you have an 801 "pen-style" atomizer, then you can pop the white reservoir off, because you don't need it). You'll get several good vapes before you have to drip again. That's all there is to the basic process of dripping!
Now, let's get into the details:
FLOODING:
If you hear a pronounced gurgling sound while vaping, and you're not getting much vapor, then the atty is flooded. There is a small heating element in the bottom of the atty, underneath the bridge. If it's drowning in liquid, it can't get hot enough to make vapor. Remove the atty, and blow the excess liquid into a paper towel. You should blow into the large hole, and the liquid will come out of the small hole on the threaded end. Keep blowing until very little liquid comes out. Wipe it clean, and don't forget the threads. Replace the atty, and try again. You may actually need another drop of liquid at this point, but try it first.
BURNT TASTE:
If it starts to taste burnt, the atty is too dry. It needs more juice, so give it another drop or two. You can avoid this foul burnt taste most of the time by paying attention, and learning how your atty behaves. Try to remember what it vaped like just before it started to taste burnt. Likely, there was a lot of vapor, but very little taste or "throat hit". Next time it vapes that way, give it one or two dropsbefore it runs dry.
CARTRIDGE MOD for DRIPPING:
This is unnecessary, but will save you a lot of aggravation from removing/replacing the mouthpiece each time you want to drip. A lot of people just "tailpipe", or suck directly on the atomizer. The 801 style is more suitable for tailpiping, because it is longer and doesn't get as hot where your lips touch. This mod doesn't work on "whistle tip" style cartridges. Because the tip is so narrow, it's hard to drip through.
1) Remove filler.
2) Shave a mm or so off the atomizer end, so no worries about melting.
3) Remove the inserts from the mouth end. These are the two small plastic disks with holes in them, and they are in the end you place in your mouth. You can lever them out with tweezers, a bent wire, or you can screw a sheetrock screw into the hole and pop them out.
4) Cut or drill out the bottom of the reservoir (you can hold the cartridge with pliers to keep from cutting yourself). The reservoir is the part that held the juice and the filler. Make sure to get all the little plastic pieces, or shavings cleaned out. What you wind up with is a (mostly) empty tube without anything to obstruct the juice drops from falling directly onto the bridge. If you look through it from one end, it will look something like this, depending on the style of cart:
It needs to be cleaned every now and then, but that's the only time it needs to be removed.
ATOMIZER MOD
If you have problems with carts that don't fit your 901 very snugly (they are probably 510 carts), just get something like these Kobalt 8" long-nosed pliers from Lowe's:
Put the very end, just a mm or so, of the cart end of your 901 atomizer into that circular void by the cutting blades. Squeeze very gently until you see the tiniest bit of flex in the metal. You're not trying to make a visible change to the atomizer, here, just flex the metal a bit.
Now give the atty a 1/4 turn or so, and do it again.
Test.
After doing this, my carts fit almost too tightly, but that's perfect for dripping. There should be no visible sign that you have done anything to the atty.
T-Tip
Alternately, you can buy one of these machined brass T-Tips, designed for dripping.
There are also various other devices, like the grip portion of certain ink pens, that can be put over anatty and function as a mouthpiece.
Also, I have one of [these] . I think it makes dripping even handier, because I don't have to mess around with screwing and unscrewing bottle caps. I just squeeze a couple of drops onto my atty, and vape! I have the small one, which is about as tall as the width of my palm.
It's not perfect, because:
A) It's pretty darn big.
B) It's a bit expensive for a little pump bottle.
C) There's a (surprise!) small learning curve because a full pump stroke delivers enough liquid to flood your atty. You have to learn to partially depress the pump. I have made a small modification that seems to work fairly well: I pulled the cap off of the pump tube, and cut about ⅛" off of the end (NOT the end that is inside the bottle) with a razor knife. Now it usually gives me one big fat drop, about the same as 1½ to 2 regular sized drops from a juice bottle. Use care when doing this, because the plastic is very hard. It takes a bit of force, and the plastic will "give" all at once. Also, I imagine I got lucky with the length of tube I cut off. I think that if I had cut much more, it wouldn't work at all.
D) The inner bottle can be difficult to remove. I solved this problem by using very fine sandpaper to sand down the little bumps inside that hold the inner bottle. Note, I'm not talking about the two large, semi-circular ridges. Oriented just above the gaps between those larger ridges are two smaller ones. They are kind of hard-to-see, but they are easy to find if you feel around with a finger.
Dipping:
Dipping is a similar concept to dripping, except you get the juice onto the atomizer by dipping the bridge of the atomizer into a container of liquid. Contact lens cases are popular containers for dipping. Dipping fans claim that the method delivers exactly as much liquid to the atty as is needed, so flooding is not a problem. Since I don't use that type of atomizer, I've never tried it.
Of course, dipping only works with the type of atomizer that has an "exposed bridge".
