This kit is an intake improvement. If you increase the ability to flow air through the intake side, you *must* improve the flow of air through the exhaust side. This GoPowerSports kit is all about the intake side so you need to have some comparable improvement to the exhaust side. I would think the instructions with this kit would tell you what needs to be done with the exhaust side. Which I suspect is probably another "performance kit" from GPS. If this kit is designed to run with an open header pipe and you're running some kind of muffler ...especially if it's the stock muffler ...you're gonna have big time jetting/mixture issues. If you haven't made exhaust flow improvements, the engine will run rich ....which explains the wet, fuel fouled spark plug. A wet plug will generally not fire so don't check for a spark using a wet plug. The rules are the same for any engine, the 212CC Predator or a 455 Pontiac, if you improve one side of the engine (intake or exhaust) you must improve the other to get a properly running engine. It's even more poignant when dealing with just the intake side.
My advice? Pull off all the "performance mods", set things back to stock and get the engine running good in stock condition. If you have a California EPA carb (one not adjustable for idle mixture and idle speed) then drop about $18 and score an adjustable stock carb off Amazon. This may be part of your present problems. Make small, one at a time, improvements to the engine. You can get a lot of improvements that don't cost you squat with the stock engine. The stock intake can be improved by simply opening up the stock air cleaner box. The stock airbox is highly restrictive; cutting a 2" x 3" hole in the outer side of the airbox will improve breathing; stock main jet works if you leave the stock muffler in place. Go with a less retrictive exhaust and you'll need to get a slightly larger main jet. You can get a safely higher revving engine by making smart tweaks to the governor system ...plenty of info/how-to's on YouTube. IMHO, do not gut the governor unless you are gonna "blue print" the motor with a more robust con rod, balanced flywheel and higher spring rated valve springs. Otherwise you're tempting the fates. This is a "lawnmower" engine and designed for low performance and high longevity.