wrong oil

So I buy these nice looking pair of 97 sea doo gti. They look brand new except for a little hull damage on one. But I think I can repair so I pay 3500 with a nice double trailer. Which I k ow is a little higher than book. But I look inside and the things look New! Guy claims he's had them...

Alright so here is the thing, this seadoo has been giving me trouble for the past 2 weeks. It runs rough and wont go above 5000 rpm on the water. Idles at 1200 rpm. Smokes like a chimney. It is the carb model. The front spark plug is wet the back it dry. It got filled up by "somebody" with...