Does ANYBODY read this site at all??

Getting nasty is a good way to get advice..............

I wasn't trying to be nasty. I was serious. It seems like low traffic.

This is one of the slower forums.

I don't think gluing PT wood to non-treated wood is a great permanent solution. I'd lean toward something like cutting all the joists off and re-framing the whole porch with a PT structure.

How high is it off the ground? Do you have a photo you can post?

I have no photo, but it is a narrow porch and is supported by itself, as the joists support the porch deck. There are no beams holding it up.

I understand the current structure is cantilevered. My thought would be to put a few posts in the ground, a ledger board against the house, and new joists, all out of PT.

Another alternative, if you've got access inside the house below the porch level, would be to sister new joists to the rotting ones, securing them well inside the house.

OTOH, if it's been 50 years, the joists still feel very stable structurally, and you're just dealing with 1-2" of rotted joists that make the porch floor springy, then you could probably extend the life cheaply by sistering PT 2x8s to the exposed portion of the existing joists, after cutting out the rotted portion.

Just determine what's going to show and what's not. Go with what weedyacres said. It's a choice between patching and R&R.

If I sister on each side of rotted joists, is there an epoxy, or something I can put between the sisters,and on top of the original joist? Also, is there a membrane,or something I could put over the joist and the sistered 2x8s?

You don't need to sister on both sides; one side is sufficient. No epoxy needed, just nail or screw them together. You could put a waterproof membrane (like window flashing or something) over top of the joists to prevent future water damage. But keep in mind that PT wood is treated to withstand water and insects, so it shouldn't have the same rotting tendency of the original non-treated wood.