MAKHQ - I have an HQ Avante - there are some great youtube videos by the HQ Educators on tension that might help and if you are on Facebook there are several techs and Educators is the HQ groups that are wonderful.
So not knowing how familiar you are here would be my course of action if it were me and my Avante. (My only concern is your comment about the bobbin thread being hard to pull up which might indicate other issues)
a mess on the back usually indicates a top thread issue. Remove the top thread and completely re-thread it. Make sure that it is firmly seated in the tension disks, Now down to the needle .... What thread are you using and have you chosen the correct size needle. I use mostly 18 or 20. Is the needle in correctly? fully seated (I think the 16 has a "sight hole" to see if it is inserted properly) and is the grove to the front? I might test it here.
If no luck - Next I would remove the bobbin - clean the case and make sure that the backlash spring is inplace and the there is no lint inside that case or under the little flap the thread snaps under. Also check to make sure that you do not have thread or lint anywhere in the bobbin area. Use a new bobbin - and be careful that it is wound evenly and is not overwound or loose ... I usually underfill mine when I am chasing an issue. If it is a prewound bobbin, I have found I sometimes need to remove several yards as they are too full and my machine does not like them like that. Also if it is prewound and a Magns Glide I remove the backlash spring.
I hope some of this might help - while I have had my machine for several years when in a hurry I sometimes miss something - a day away from the machine always gives me a better perspective! good luck - let me know how you make out.