Wrong air filter adaptor

I have recently bought a go kart and I’m very new to them. I’m looking on ebay for an air filter to fit on my Briggs and Stratton 5hp engine but all of the adaptors are the wrong size. I need a 31mm adaptor but they are all 23.8mm. Does anyone know where I could get an adaptor that has the size I need or how to modify the adapter to get it to the right size?

thank you very much!