I have some improvements to try, but I have a hard time understanding how it is so bad. Wondering if there's something I am overlooking.

I've tried with two beans. One was roasted 10 days ago, the other 6 days ago. During pre-infusion I get almost instant drips, and when I pull I get very little resistance. A couple of times I got some good "udder squirts" but still wasn't ideal. I can easily burn through the whole shot in ~5 seconds.

I'm using an older grinder that I know is not great. It's a well used Starbucks barista conical burr which I understand to be similar to some other models. I've tried the first few clicks of the finest settings.

My next attempt will be to go to a well known local roaster to try fresh beans that they grind.

I am also going to put together an old Rocky Rancilio with new burrs and the typical upgrades.

I'll update after I try those new things, and I've watched the videos/etc., but it seems so far off that I'm wondering if there's something else I'm overlooking.

I also believe it is your grinder.
Get yourself a decent one and start again.

You can adjust the grinder to your machine and your taste.
That is something a shop can not do, therefore pre ground coffee is not a good idea (apart from getting stale).

I know it's not ideal but I'd think my old Rancilio Rocky with brand new burrs has to be an upgrade, but it's still relatively the same as the other grinder at or near the zero point.

I do imagine that I should be getting finer grinds (it feels more granular than what I would describe as something between salt and flour), so I'm going to get some ground at the shop down the street to rule out the grinder. I know it won't be great for taste, but should at least let me practice.

The problem with getting it ground somewhere else is that you are stuck with whatever grind they give you. Dialing in the grinder is an essential step to making espresso. If you can't get the grind to match your machine, and other environmental variables in your kitchen it will be hit or miss (most likely miss).

The grind quality isn't just about the size of the particles, but also the consistency throughout the dose. New burrs on a badly aligned grinder will produce questionable results. If you have a more consistent grind with the Rocky it should be better. Also, you might be able to mod the Rocky to give you finer grinds than it does now. I know that it is not highly regarded, and a better grinder is probably in your future.

Agree with all if the above. Having beans ground at the shop is no way to rule out the grinder. You're more likely to have similar gusher experiences, not just bad taste. What they think is "espresso grind" will not be pavoni grind. I tried it briefly in the beginning, fully aware it wouldn't work, and I can't recommend it.

The only way IMHO would be to find a grinder you can borrow, go with the machine to the shop or at some friends with a grinder (yeah, covid times I know..), or perhaps get a good enough handgrinder though they can be quite pricey.

I admit I got myself a cheap Hario Skerton, which I completely realigned, to POC the hobby for myself before getting a proper grinder.

One other potential thing overlooked on this thread is the grouphead temperature. Even though I don't think it'd make that big of a difference I would like to ask are you heating the machine enough? I always advice new La Pavoni users to get a grouphead thermometer, it is the most important "mod" for these machines.

I thought the Rocky was decently well aligned, but I now have a theory that the shaft might be bent. There's definitely something out of whack. Taking it to my machine shop buddy soonish.

Borrowed a cheap grinder from a buddy that seemed to be grinding decently enough and did manage to get a semblance of a good shot. ~10 second extraction was still fast, but I had a proper puck until a channel formed

Here's my best shot so far. Seemed to be really good until a channel developed, and then it blew out after ~10 seconds.



Still more to be learned, but I feel like there is hope!