Ok, so just this morning, I picked up a 1990 Polaris Indy 500. The engine has a couple little quirks, here's my best description;
The first two or three times I started it, it started right up, and idled well. I revved it a little bit, but never tried to move it.
The next time it started, it idled at around 500 rpm (warm, it should be 1900), and I tried to get it to move, but it would get to 2000 rpms, and just bog down.
Now, it needs the throttle held in order to start, and it will stall if you try to let it idle. It will not peak 3000 rpm. It will slowly accelerate to 3000, then just stop, you can hold the throttle all the way and it just sits at 3k.
The previous owner had damaged the kill switch, so he had been using the choke to kill it (flood). The spark plugs do appear to be fine.