1) Has this unit been stored for a period of time of disuse?
2) Was it stored with E-10 (ethanol fuel) in the tank?
3) Did you use fuel stabilizer?
4) Was the tank full or empty during storage?
Plugs don't go bad just sitting. If it was running well and stored and trouble began after storage it's doubtful that the plug is the culprit. Inspection of the plug should be enough to determine whether it's fouled.
Fuel pumps do go bad. Obtain a fuel pressure gauge and check fuel pressure. Compare to specs in manual. Even a new fuel pump could be defective. Tests confirm.
Get a manual if you don't have one. There are digital downloads for most models available on line for about $10.
If it was stored with ethanol fuel simply draining the tank and replacing the fuel may not be enough. In addition to Phase Separation, ethanol fuel also damages rubber parts and even some metals. The fuel lines may have begun to deteriorate from within with no visible exterior damage. Small particles of damaged fuel hose may be clogging injectors.
Polaris states that 80% of electrical problems are due to poor connections. Corrosion, damage or dirt at the connections or wires damaged by vermin could be the problem. Inspect all wiring. Manual should tell you how to test EFI electrical components (Sensors).
I don't know whether 500s had the problem, but some engines had a problem with a wiring harness. (I think it may have been 700/7800 engines)