ATV runs rich, won’t idle, but will run hard. Throttle body is black like carbon/soot.

I’m going to replace spark plugs…anything else to check for or replace?

Also, is there a cheaper place to buy equivalent of Polaris Oil, spark plugs etc?
Beings I’m on SS just trying to save $$
But I definitely won’t take short cuts if it will damage my machine!!

Thanks,
Tim