Drk14

Hello, I am trying to work out the kinks on a 2004 Polaris virage that has been sitting out for most of it's years. It is not mine but the owner is letting me make sure it is running properly so he can sell it to me for $2000.
The jetski only had 5 hours on it when I first started testing it out. But I noticed after a sort time, like an hour or so it started acting up. At this point it will not allow me to rev past 3000 rpms and the engine sounds like it is bogged down. For some reason occasionally if I turn the engine off and let it sit for a bit it will start to work right but shortly starts acting up again. I have put in premium gas and the right oil in everytime I have taken it out. But it has fouled out a few sparkplugs in the rear cylinder.
I have also checked the compression in both cylinders and they are the same. The jetski is in great condition like it was brand new because it hasn't been ridden but it does keep fouling the rear spark plug and I'd like to get some advice while I have another weeks wait before I can take it to any shops around here. Thank you.