Do i dose too much coffee

[yosi]

i have a 3 group la san marco i am using 9 grm porta filter and grinding coffee per shot
the stream of the coffee is very uneven at times and sometimes sprays all over in very strong streams
i am using a bottomless pf holder when i am dosing into the 14 grm pf its so much better the stream is steady the crema is perfect should i not use the 9 grm pf any more ?
is 14 gr extraction for 20 sec not too much coffee for single espresso
i just always knew that single shot is 7 to 9 grm am i wrong and why is the stream of the coffee going crazy when i am using the 9 grm
i can always see the head screw in my grind is that ok ?

[cannonfodder]

You may be overdosing. Single baskets are finicky IMHO when it comes to the dose. If you get too much coffee in there, they puck surface may be scraping against the shower screen when you lock the portafilter in. That will break up the puck and cause channeling which is what you are describing. The dose is also machine specific in many instances.

Here is a test for you to try. Dose and tamp like you normally would, then place a nickel on top of the puck. Lock the portafilter into the machine, and then remove it. Is the nickel smashed into the puck? If so, dose down a little more. Once you get to the point that the nickel leaves a very light impression in the puck surface, you are there. Then adjust your grind and start pulling shots. Most single baskets are also shallow, so if you go to low, your tamper will be bottoming out against the basket and you will not get a good tamp. I think a concave tamper works best on single baskets.