deckrailing
It appears more drastic in person. This deck railing is leaning inward, and I'm wondering how one might go about leveling it up? Willing to replace 4×4 supports if necessary. The posts towards the middle of the deck slant the most, but it is very inconsistent overall.
Around here, 4x4s are not uncommon. This table shows that a 4x4 pine post that is 6 ft or shorter can support a load area of up to 10 ft² assuming 50 lbs/ft².
Don't trust me or a random table on the internet; make our own calculations from tables in the building code or other trusted sources and consider having them checked by an engineer.
There are lots of different types of post to beam connectors.
Like this:
However, the real weird thing is that you don't really have beams. They are just supporting the joists with a bunch of random posts on concrete deck blocks...
If it were me I'd lose all of those and put in a couple (or more) beams under those joists and put some posts under those.
Not in that order, though. Leave the posts in, put in some proper beams and posts, and then lose the crappy ones you have there.
Below is an example of a similar height deck I did. There are two beams under the joists of this deck, and four piers (two for each beam). The beams are the ones with the white flashing tape on top. You can clearly see one in this image, and how I attached it to the joists.
Best Answer
If you were to replace all the lag bolts, you could play around with plumb by shimming the top or bottom of the post where it sits on the rim joist. Be sure to use galvanized bolts (and healthy sized washers on both ends) that go all the way through the post and the rim joist.
A very big caveat: this might have met code where you are, but a 2x4 post -- especially an old one -- isn't the sturdiest. The IRC requires that a railing can withstand a 200 pound load in any direction. I would think seriously about replacing the posts with 4x4s securely bolted to the rim.