Polaris 90 wont achieve top speed?

My polaris 90 year 2003 will not achieve the pretty 30-35 MPH it usually tops out at. In fact the engine sounds choked and runs at 10. I took off the filter cover (fuel filter it appears) and it was dirty with mud and stuff all around. I didnt please parents asking for help, always busy with something else. Can I buy a kit I am looking at on ebay right now (look in links) to replace the dirty filter and have her running like new again, or may there be another prolbem?