I use the Joye 510 cartos exclusively, and I've used them for about two months. I've bought about 50 of them, and maybe 10 have died in that time from one cause or another. I've dissected them, performed autopsies if you will, and I've picked up some maintenance tips, and even developed a few myself.
If the carto tastes burnt, even with plenty of fresh juice in it, it's most likely because it got vaped until it was dry at some point and the wick of the atomizer has gotten scorched, perhaps some of the filler next to the atomizer too. If that's been scorched, any delicate flavors will probably have a scorched taste in that carto from now on. You might still get some mileage from it with a heavier flavor or something that wouldn't taste bad with a little scorch in the background. That is one thing with these cartos, you really have to be careful to stop vaping them as soon as the flavor gets weak or scorchy-tasting. If you are careful to avoid scorching, they can last a good long time and may never need cleaning. Remember, cartomizers are intended to be disposable, so getting a few weeks good use from them is still money ahead.
If you want to wash out the Joye 510 carto, including the filler material, there are several methods. DO NOT BOIL THEM! Boiling will cause several problems with them. You'd want to be sure and remove the mouthpiece and the little barrier piece so that air and liquid can pass through the fill port where you put the syringe. Some people open them up like that then let them soak in warm water overnight, then blow them out, using varioius methods.
When I want to clean mine, I use a plastic syringe made for giving liquid medicine to infants. It comes with a rubber cone that attaches where a needle would otherwise go. This syringe is available at most any pharmacy. That rubber cone is a perfect snug fit for the 510 carto. Just put the carto into the rubber cone and draw warm water through the carto with the syringe, then push it back out. Do this several times until you consider it flushed out adequately. Then you can pump the syringe into the sink a bunch of times, like maybe 50 times, to force the water out of the filler material. Some people then place them in front of a fan, or in a sunny spot, or on something warm for a day or two until they are dry.
I've also used this same flushing method but using Everclear grain alcohol. Sometimes I do both in one session. The Everclear will dissolve anything the water doesn't. The alcohol also dries very quickly, as alcohol does. It will even dry out the water if you do water first then alcohol. Some people think the alcohol leaves a bitter taste, and some have said they do the alcohol first, then flush it out with water.
I've also used a bicycle air pump to force air through the wet carto, and there are other ways you might devise or adapt to dry out the filler material before re-using the carto.
Overall, I'm not at all sure it's worth all the trouble to clean them, unless you are really tight on money. I figure I could use all brand new cartos one time and toss them and still save money compared to what I spent on analogs. But I am refilling all my cartos for myself and my wife every week, and they are getting refilled at least 10 times on average, maybe lots more because I've kind of lost track. But they last quite awhile if you don't scorch them.
