title_body: What is wrong if my espresso pours out slowly but the first drops shoot out?
upvoted_answer: Looks like you've got too much ground coffee in the basket. What's the weight that you're using? It looks like the recommended dose for the stock basket is 14g, which is a bit lower than the "standard" of 19g or so.
  
  You have an indentation (ring) around the outside of the grounds -- an indentation from the group/dispersion screen (in addition to the notorious protruding center screw on this model). If you're already tamping thoroughly, this could mean you've got too much coffee in there.
  
  Here's a thread from Home-Barista on the Silvia around a similar topic. It discusses another way of diagnosing the dose -- inserting the PF with tamped grounds, then removing while still dry. 
  
  That article also talks about aiming for a dose+tamp to leave a bit of space between the tamped grounds and the screen: approximately the thickness of a 5-cent piece of space (1-2mm), which is a general recommendation (not just for this machine), though there is certainly disagreement on this. Another article from Serious Eats discusses this topic and notes that a "sludgy mess" can result, because the grounds will expand a bit when they absorb water. Your picture also looks a little "wet"; it could just be the picture, or perhaps a similar symptom.
  
  Try a lower dose (14g) and do the dry-removal test, aiming for a bit of space between the top of the tamped grounds and the screen.