Midrange fuel (25% to 75% throttle) is delivered from the main jet via the needle jet/jet needles. How are the needles set?
The 96 SKS 500 was either carb or EFI, the carbs should have had an enrichment circuit (chokes). The primer is probably after-market. Can you post some pics of what you have? That way we can get on the same page with you.
Here's a link to the Polaris website for parts diagrams, it may help you as well...