I am new here and after doing a bunch of reading on the site I thought I'd just come right out and ask; What's the general consensus on these 250 Odyssey engines? Is it worth my time digging into this thing, which most likely needs at least a top-end rebuild, or is there a Rotax swap in my future?

My dad has agreed to sell me his FL250, which he ALWAYS had problems with fouling plugs and he usually had issues with it being hard to start my whole life too. Our family is pretty mechanically inclined, so knowing the usual suspects he had gone through & cleaned the fuel system which I'm guessing included the gas tank, filter, old lines and definitely the carb. Many, many times he was tearing into that carb, it seemed like he was working on it every year, or each summer whenever the kids wanted to bomb-around up north in that old Honda. BTW I told him to knock it off with the ether and start using marine fogging oil instead, it's much safer - especially on 2-stroke engines. Learned that trick from a tech who used to work here when he helped me replace the driveshaft seal on one of my kids JetSki's. What a pain working inside those things! I'd rather work on an MX bike or quads any day of the week...speaking of quads, I gotta get back out to the shop and finish up replacing the one-way clutch bearing on my Uncle's Can-Am and wiring in a new LED taillight for him so I can get the heck out of here before midnight. I'll check back in tomorrow or Thursday for any replies.

Thanks in advance for your input,
Chad in Wisconsin

Ok I'll comment.
You can just forget about a rotax swap.
The FL250 has no suspension and no real frame or proper roll cage or suspension seat or -- and the list goes on.
The swap would cost a lot of money you would not recover in a sale and it's just unsafe.
Lets move on.

Fouling plugs:
I bet my rent money you guys are mixing oil/fuel at 20/1 ratio. That's WAY to rich.
You may also be running a very cold plug.
Today's oils are not the same as the oil in 1985 and neither is our fuel.
Now a days even chainsaws are mixed at 50/1 with the new oils. I don't recommend this unless an oddy is liquid cooled. Bet you are still golden at 40/1 with air cooled.

In my opinion I would leave it stock, do a rebuild and mix oil 40/1.

Just my opinions.
CO

Edit:
Hard to start. How old is that machine ? Is it a points system ?
Verify it's all set correctly.
Maybe use a shot of either.
CO

My first fl250 had a tune pipe so clogged it took a torch to get it cleaned out. Like CO said, it was from running too much oil. There was a sticker on the buggy that said to run 20 to 1 and the previous owner didn’t realize that sticker was put on there from the factory back in the early 80’s.