Problems with Rancilio Silvia: How could I prevent getting too much or too sour espresso? 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?
That's a pretty extreme contrast for a one-level difference.

A couple things you could try:


Use slightly less grounds if you're on level 23 - this will make your puck a bit easier to push water through.
Weiss Distribution Technique - use a toothpick to break up any clumps you have in the grounds before tamping - try this on level 24, since you may have some channeling going on with the slightly coarser grounds.
Pre-infuse your puck with grounds from level 23 - soaking them a bit early before starting the pull may help you to get a proper extraction. See this youtube video.