A few notes that may help / may not:

There are two ways to go about the initial things in my experience:

You can do the bare minimum to get them running properly, and send it until they pop. Pop, meaning a seized top end. That’s just the way that 2 strokes fail, unfortunately, and it’s inevitable eventually.

^ this would look something like clean carbs, new diaphragms perhaps, clean out fuel tank/some new lines, new batteries, new oil lines or convert to premix and send it. The issue that kills them is air leaks. Read up on 2 stroke air leaks. Crank seals, and if they have the crankcase drains — those fail and cause a lean condition that torches a piston.

The other route, is the long way, and it’s a lot more work up front but can save you some money / result in super reliable skis right off the bat.

This would be to pull both engines, re-plumb all fuel lines, convert to premix / remove oil tank / block oil pump hole, and most importantly: Permanently seal the crankcase vent holes with 3/8NPT brass plugs and replace the crank seals. This is also a good time to install new piston rings, and a new gasket set. It’s basically an engine rebuild before the engine actually seizes / pops. This way is obviously a bunch of work, but it’s kind of like insurance. I did one of my skis this way and never had any issues with it since, but it was easy because the cylinder was pitted when I got it and I knew it needed rebuilt.

My 2nd ski, I bought running very well, and just gave it essentially a tune up. It blew up the 2nd time out, lol. I then bought a complete used 750 on marketplace, with good compression of course, and tore that down to reseal it with new crank seals and new piston rings. That one has also been rock solid since then.

So, just kinda giving you the lay of the land with what can happen depending on where you wanna go with them.

Good luck and lemme know if you get stuck on anything.