I have a 2017 Polaris rmk pro 800 and it keeps fouling only the clutch side spark plug. Only mods are bikeman billet cooling head and ggb can. Maybe get 10-15 miles a plug. Plugs look rich when pulled. Seems to only foul from low rpm like right when it starts. Just had injectors checked and they are 100% fine. What else can it be? Check oil use and it’s right where it should be. any help is greatly appreciated.