Last night I tried my brand new Jam Monster and it was delicious.
From the description of your juice, it sounds to me to be a coil killer...sweet juices will tend to gunk up a coil quickly (1 or 2 days) the black stuff on the wire isn't burnt, it's just gunky buildup
^ This. I've tried the Strawberry version of Jam Monster and it was EXTREMELY SWEET. So sweet that I could only vape it for about 5 minutes and had to switch to another flavor. And I really wanted to like this flavor.
So as Shadav said, sweet juices like that will gunk up coils quickly. High heat carmalizes the sugars in e-liquid forming a crusty layer on the coils, and using higher wattages with sweet flavors carmalizes the juice faster. My advice is to use lower wattages with sweet and fruit flavors.
If you go with a different tank, I would suggest trying the mentioned Innokin Zenith. Its a mouth to lung tank that uses much lower wattage settings than you've been using. You could also try the Geekvape Cerberus, which I've been trialing for Geekvape for the last couple of weeks. I'm still using the original coil with a sweet fruit flavor and no problems with a burnt or harsh taste. It's a sub-ohm direct to lung tank that uses drop in mesh coils. I using it at a 25 watt setting. When my original Crown coils become unavailable, I'll probably begin using the Geekevape Cerberus tank.
Zenith tank
Cerberus tank
Unless you really want to get into the hobby, don't feel that you HAVE to use a rebuildable tank (RTA or RDA). There are good tanks on the market that use factory made drop in coils. I use the
Original Uwell Crown Clearomizer Tank, but I've been reluctant to recommend it lately because its a 4 year old tank and the availability of their drop in coils are starting to become scarce. The later versions (Crown 2, 3, 4, and Valerian) of the Crown all use coils requiring higher wattage settings than I like to use. I tend to like to vape at 30 watts or lower.
Having said that, learning to rebuild for a RDA or RTA can lead to a more perfected vaping experience and be more economical in the long run too. Read my
Information Resources for Your First RBA to see if this route might be for you.
Speaking for myself, I've done the rebuilding thing. I found most of the rebuildable tank atomizers to have a high learning curve as far as wicking correctly, and I grew lazy and tired of having to rewick my rebuildable drip atomizers every 3 - 4 days. So I went back to using drop in factory coil heads.