I have been meaning to modify my Cimbali Junior grinder ever since I saw that there were beans and grounds becoming stuck above the upper burr in the area between the burrs and the hopper. I finally went to HD yesterday and bought what is called a "1 1/2" male adapter" in the plumbing section for a big 89 cents. They had a few lengths but the one I bought was around 2 3/8" - 2 1/2". I should have measured before modifying the part, but I got ahead of myself. First thing I did was remove the hopper to expose the adjustments rings and upper burr carrier area. The inner diameter of the adjustment ring was approx. 2 1/8" so I had to shave down the widest part of the pipe adapter to slightly less than that diameter. I used a small motorized belt sander but you could do this a few ways depending on the equipment available. Once that was done and tested for fit, you need to remove some of the PVC material to notch around the burr carrier screw "flanges"(?) and this was best done with a Dremel and the standard 1/2" drum sander. You sand down three notched areas to go over where the upper burr screws to the carrier. The whole pipe adapter then needs to be cut down to length which should be approx. 2" to 2 1/8" (less if you adjust more than a few turns so it doesn't bind with the hopper throat and prevent further adjustment), and I cut the wider end so that the other end sits nice and flat on the upper burr. After that's done and everything fits nicely (should be somewhat of a snug fit to the upper burr screw flanges to hold it in place), install the hopper and that's all it takes. I added a few "after" pictures of the adapter and process below, but it took less than a half hour and the plumbing part was less than a dollar. It works great, and the problem has been solved with this mod - the beans feed directly into the burrs.
The pipe adapter, after modifying
View of the adapter bottom with three notches
The Dremel drum sander for the notches
Another view of the modified and notched adapter
The upper burr area, as it comes from the factory
The modified pipe adapter in place
View of how the pipe fits over the hopper throat (too snug of a fit will restrict adjustment)
Hopper in place, modification complete
View of beans in the modified throat (mmm...Kid-O)
edited to add a few more tips to the instructions.