I would call the guy and ask him about the spare parts. If he's swapped a lot of stuff out (not knowing what he's doing), I probably would go for a new carb. Oem's are probably under $100.

Your buggy motor will never reach its' full potential without changing the filter. Build a splash guard or try to snorkel or something. Besides, you should never be running a buggy in belly button deep water, which is a little higher than a stock or redneck intake on a gy-6 150.

I not to worried about burying the thing in the water, I just don't want the water splashing on a aftermarket filter to be an issue. My brother in law rides a Banshee. He's got an aftermarket filter with an outerwears on it and if he rides it through a puddle it runs bad for a few seconds from just the splash.

Does this issue sound like it is more than likely a carb thing, or could it be something bigger? What would be the symptoms if the valves were out of adjustment?