I bought an older Rancilio Silvia machine and try to adjust the grind of my CM90 grinder.
On grinding level 24 I get with 15g powder after 25 seconds 73g espresso in two cups which is way too much (it should be 35-40g).
On grinding level 23 the machine is able to get any espresso if I tamper normal. If I barley tamper, I get 27g Espresso after 25 seconds, but it tastes horrible sour.
I do temperature surfing and wait 0 to 20 seconds after the heating phase before I start the machine. I tried different beans which are 1 to 3 month old.
Any idea what might be the problem?