I purchased the lawn tractor second hand and it has been sitting a long time. The carburetor was not getting fuel and the valve that is operated by the float was stuck. I cleaned got the carburetor operable. I started the engine and it started right up, but the it would not start again. It was then not geting any spark so I used a scocth brite pad to clean up the area where the contact is made to create the spark. Not sure what it is called. I am still not getting any spark. How do you check to see if the part that has the spark plug wire attached is not working? Is there a gap that needs to be maintained?