or at least, that is my suspicion....

After replacing the old spring with the new stainless spring I am battling with very frequent eruptions of portafilter sneeze starting during first part of extraction. Needless to say that this ruins the espresso but I am getting a bit tired of having to make several attenpts at a cuppa, and getting burned in the process.

So I fiddled with:
the sleeve, screwed it slightly tighter>no result,
the basket, removed the tinfoil keeping it in place lacking a spring clip>no result
Both gaskets (mine has a thin gasket combined with the thick PF seal> no result.
Tried an additional very thin rubber shim like gasket, but was unable to get the PF locked in.

The PF locks in at roughly the same place as before, and the eruptions occur suddenly after approx the first 1/5th of the lever action imo the point when the pressure is at its peak.

So before I unscrew the beast again to test with the old spring I would like to see if anyone has some advice, I sadly do not have a spare PF seal, but might have to order one on the quick but somehow it seems OK..(6-9months in place, used for something like 10-12 doubles a day)

Are you not able to hold the portafilter in place while pulling the lever?

Holding it in place? It gushes out between the two, or more likely between the grouphead and the seal, even if I lock the PF a bit further..the force is such that The whole shot is emptied in a matter of seconds...

Might be that I tightened the sleeve too far....that would make the seal less thick....

My apologies, I misinterpreted what you were describing.

Yeah, I would back the cylinder out a bit - it sounds like your PF gasket seal has been compromised. I suspect that's more down to fine tuning the cylinder height than additional pressure from the new spring. It seems unlikely that you have increased brew pressure so dramatically that it is blowing out your gasket.

FWIW, I had a hell of a time getting the PF gasket set just right in my Comocafe, another machine with an extremely strong spring. It required a very precise setting of the gasket, but it's been fine for 18+ months since I dialed it in. Before I got it figured out it was behaving much as you describe your Faemina - spraying coffee everywhere mid-shot.

I got seals from both Francesco, and OE, and I think I ended up choosing a thicker PF gasket that came with one of the sets. This happened to me, during a test run it blew out, and then I changed out the gasket and it fixed the issue.

Are you cranking the cylinder back up in there, or is it essentially just hand tight? If the cylinder rose higher in the grouphead than before you did the spring swap, the PF gasket will be higher up and a gap may appear.

Think I just fixed it, I unscrewed the sleeve by a bit (of course initially too far, causing a leak)...
First cappuccino of the day

So far so good, caffeine levels are back up

Thanks for the advice folks!

Now the Vesuvius issue is resolved I dare say that I'm pulling the best shots so far.
Shots are thicker, more complex and more balanced at the same time. Think I can grind a bit finer so will try that to see what that brings.
Can't wait until my new stash of beans arrives tomorrow..

I went through the same sort of thing, after reassembly it gushed from the group. Tore it down again and it seemed the cylinder wasn't tightened all the way in. While at it I decided to just replace all the seals and gaskets. Reassembled it again, making sure to double check every step, and now no leaks. The new spring definitely feels stronger when pulling a shot, and it seems to have increased the shot pressure. Crema and mouthfeel have increased. For the modest price Paul is charging, a very worthwhile investment.

This time around I also used Francesco's scissor jack method instead of a clamp, much easier and less stressful. Not having a jack sitting around, just borrowed the one from the car.

A small machinist jack works extremely well.