Troubleshooting Espresso Machine (Isomac Super Giada)

SpicyRiceTea

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Jan 30, 2020
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I recently purchased a second hand Isomac Super Giada as my first espresso machine and I've been encountering issues pulling shots on it.
Given the 53mm size of the portafilter, I've only been filling it with about 15g of grounds, and I've been aiming for 30g shots.
When the pressure reads 8-9 bars, the shot time is only 11-17 seconds, and it's a sour mess.
When I go finer, the pressure reads 11-12 bars, the shot time is around 22 seconds and is more palatable, HOWEVER, there's a considerable leak between my portafilter and the group head.
Since it's my first machine, I don't know if that's normal (because the pressure is too large) or if it's an indication that the gasket due for a change.
I'm thinking it might be the latter since I can't imagine what else I can do to make the shots last longer while still outputting a 1:2 ratio.

Also, I know that usually, the ideal pressure to pull a shot is 9 bars, but when I use the pressure reader and adjust ground size for 9 bars, it pulls too quickly and the taste is awful, should I just aim for time then, even if the pressure is reading at around 12 bars?
My understanding is that give a fixed brew ratio, pressure and pull time only have ground size as their independent variable, that is, you can only change pressure and pull time by changing grind size. In other words, if a 14 second 30 grams shot happens at 9 bars, making the shot last longer while still only outputting 30 grams will necessarily require more pressure. Is my take correct on that?

Are there adjustments I should be making to my recipe, or is my gasket the culprit?
And do you think my pressure reader is accurate given what I've said?
Cheers,
 
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