What causes the fuzz, when prinintg Hoodies?

hm no idea.
I've never had that type of trouble, theres normally "hairs" on the finished product of hoodies but ive never seen it in a sense where it put down the quality of work or mad it look bad.
Perhaps its just the hoodies your printing on? It could be the weave or thread?

Try pre flashing the hoodie. This will also keep it from moving if you intend on printing a second time.

Bill Hood is a good dude: http://www.youtube.com/watch?v=CtLvG0X3_JU

In my short experience, and only with automatic press (not that it matters in this case), I have deduced that it is static electricity that causes the fiber to stand up off the substrate. And yes it is harder to cover these fibers, once they stand they tend to not want to lay back down. You get the same effect on t-shirts, it's just not as visible. Thinner substrate. A cotton hoodie would have more available fiber to stand up. You have to also imagine the image area. the greater the coverage the more noticeable it will be to customers.

A shorter flash will help as you've discovered. Basically it just gives the garment less time to become charged electrically. however then you end up with messy build-up on your screen and possibly ink not laying down. There is a happy medium in there somewhere. You've got the right idea though with the double stroke/flash/then single stroke.

Bill Hood is a printer in Texas, I believe, he has a couple videos on youtube on how to lay down a good thick layer with one stroke no flash. We've found that it works well as an underlay, but to get good, solid coverage a flash and second highlight coat are usually added (unless we are going for the distressed look). Check him out though, the video will give you some good pointers on laying down a single thick coat. **This will help you lay down a thick enough coat for an underlay (less friction to cause static charging from the squeegee), then you can shorten your flash (less ink than two strokes), and another of those thick coats gives you a nice topcoat to finish it up, and get the rest of the fibers to lay down. Don't try to mash the fibers down into the shirt, but a moderately strong squeegee pressure is ideal.

with either of these products over flashing will result in some what of a rougher laydown anyway soly because of the dulling paste or small amount of blowing agent in the chemistry. i would base down the ink maybe 10-15 percent and lower your off contact tp literally right above the garment...whats happening is the release of the screen from the garment is causing the fabric hairs to lift up. as printing tees the key to underprinting is getting a smooth matt laydown..you know that though..i may even throw in a 80d squeegie. just my .01

You'll see much improved results with the fuzz if you run the fleece through your dryer before you print them. It takes extra time but it helps this a lot.