Ykk standard zipper chain is garbage. Every zipper I made with this had your same issues. I tried everything, paraffin wax.. and I did notice that with one way zipper chain you must instal the pull going the right direction for smooth operation. This didn't help me. They literally wouldn't work at all. But you get what you pay for and if you felt the teeth on the ykk standard chain they were really rough and sharp! (not good for smooth operation.. this is why nylon zips are so smooth)
Enter Buckle Guy - I spent about 400 on Riri zipper size 4 and 6 one way chain. This was before they switched everything over to the combi chain (2 way zipper teeth) and I had much better success with that. But sadly their one way chain also has issues.
All zipper tape has lines on it marking different spacing options. This was when I discovered zipper guide to help me glue my leather at the correct spacing for the zip to work smooth as butter. If you buy a zipper guide it's a little easier but I have had a lot of luck with just gluing up to 2 mm away from the edge of the line I want to use on the zipper tape (so glue won't show after you stitch the leather to your zipper tape. Riri zipper tape is also the softest weave fabric that absorbs glue great and has multiple spacing lines. I also find that the teeth cut easier than ykk. They pop right off leaving the zipper tape nice. And if my pliers ever catch the tape I just take my lighter and clean up the tape after removing the teeth with a couple quick passes to burn away all the fray and mess.
RiRI combi teeth are great and shouldn't give you any issues! Ykk Excella also have great reviews as other lux zip brands like Lampo. I will say I wish I had those fancy Riri zipper stop pliers. They look awesome! Not sure they still make them. I recommend Buckleguy because they now carry all Combi teeth. They have many tape colors and teeth finish options compared to other suppliers. And honestly they have the best price on zippers and all the needed add ons like top and bottom stops, pulls and spacers!
