Hey,
I was having blade mount issues with my new boots and blades and here is my advice: a good tech is worth their weight in gold. Not only did the tech I went to fix the problem but he passed on a lot of info, so here we go... I'll pass on what he told me
First off, throwing up snow is a signal that the blades aren't straight - I had the exact same problem. Something is 'pulling' because the blade does not want to go in a straight line.
I would suggest bringing the skates in to a reputable shop or tech but, if you're far away from that type of service, there's a way to eyeball if your blades are atleast 'straight' and judge whether the time and money are necessary. First, you need to find the middle of both the front and back of the boot. You should be able to eyeball this if you're just taking a more 'general' look to check things out.
Now, you want to look at the back of the skate. Does the stantion (the back of the blade that leads to the skating blade... goes vertical out from the plate) match up with the middle of the back of the boot? It should be bang on center.
Next, the front... your toe pick should be just INSIDE (a half blade width) of the center of the front of the boot. Don't use the stitching to guage this. It might be off.
As for the shim, it's better to correct within the skate with insoles but if that's not possible, they can be used on skates to correct pronation.
Hope this helps. I'm no expert, but this info has helped me quite a bit... it was surprising how much a simple adjustment helped.
Keep in mind that this is just general info. Different configurations work for different people, but from what I understand, this is sort of the 'zero' point of where you start with blade mounting.