Here is a tale of woe. Whoever bought the 50 Yam (presumably from new) didn't use marine two stroke oil. They also premixed on top of relying on the oil injection.
How do I know.
1. Oil in the carbs (should have been none) and it had rotted all the plugs and seals into a black sticky mush.
2. The oil burned rather than correctly lubricating the engine. Deposits half way down the pistons.
3. The factory honing marks are still visible on the bores. Engine must be under 50 hours or less.
4. The deposits were around what you would expect at 500 hours.
5. The oil hardened the crank seals and caused them to fail.
The oil was red and had a strange smell, possibly chainsaw or moped oil.
If you want to cost yourself a fortune and have your engine last 5 minutes, that's the way to go.
Also, it had not been flushed through with fresh water, huge salt deposits round the thermostat.
Fortunately, this is fixable, but it could just have easily been beyond repair. All for the price of a good outboard two stroke and a bit of knowledge.