How are you filling them bud?
The problem with cartos can be that if they are not completely saturated before you fire, the wadding burns and that's pretty much impossible to come back from.
Is it a minging taste, or a burnt taste?
If it's minging, could just be shit juice (There are very few tobacco juices I actually enjoy) If it's burnt, you may have knackered your wadding.
One of the best methods I use to ensure the wick and wadding gets saturated is known as the condom method (all will become clear
)
Simply half fill one of the rubber ends (see, told you it would become clear) add juice to about half way up it.
Get the connection end of the carto and slowly push it into the filled cap.
This was the fluid is pushed up the centre cavity, getting the wick and the wadding.
Still worth dripping a few bits in the top depending how soggy it looks. Let in settle for a bit, blow through it a couple of times to clear the excess from the centre and away you go