Go to a local Technical School and take an evening class on small engine lawn mower repair. There are also dozens of good books out there that can help you out. Since Tecumseh is no longer in business i would first buy a Tecumseh service manual for your engine and then take it apart and carefully measure everything. Then I would see that parts need to be replaced and see if you can even get them. You should be able to get what you need but some things are getting a bit scarce. Roger